Fix uint8_t comparisons with negative values

Fix the following warnings:
/src/qemu/hw/ide/core.c: In function `ide_drive_pio_post_load':
/src/qemu/hw/ide/core.c:2767: warning: comparison is always false due to limited range of data type

/src/qemu/ui/vnc-enc-tight.c: In function `tight_detect_smooth_image':
/src/qemu/ui/vnc-enc-tight.c:284: warning: comparison is always true due to limited range of data type
/src/qemu/ui/vnc-enc-tight.c:297: warning: comparison is always true due to limited range of data type
/src/qemu/ui/vnc-enc-tight.c: In function `tight_encode_indexed_rect16':
/src/qemu/ui/vnc-enc-tight.c:456: warning: comparison is always false due to limited range of data type
/src/qemu/ui/vnc-enc-tight.c: In function `tight_encode_indexed_rect32':
/src/qemu/ui/vnc-enc-tight.c:457: warning: comparison is always false due to limited range of data type
Signed-off-by: NBlue Swirl <blauwirbel@gmail.com>

hw/ide/core.c

@@ -2764,8 +2764,7 @@ static int ide_drive_pio_post_load(void *opaque, int version_id)
 {
     IDEState *s = opaque;
 
-    if (s->end_transfer_fn_idx < 0 ||
-        s->end_transfer_fn_idx > ARRAY_SIZE(transfer_end_table)) {
+    if (s->end_transfer_fn_idx > ARRAY_SIZE(transfer_end_table)) {
         return -EINVAL;
     }
     s->end_transfer_func = transfer_end_table[s->end_transfer_fn_idx];

ui/vnc-enc-tight.c

@@ -281,7 +281,7 @@ tight_detect_smooth_image(VncState *vs, int w, int h)
         return 0;
     }
 
-    if (vs->tight.quality != -1) {
+    if (vs->tight.quality != (uint8_t)-1) {
         if (w * h < VNC_TIGHT_JPEG_MIN_RECT_SIZE) {
             return 0;
         }
@@ -294,7 +294,7 @@ tight_detect_smooth_image(VncState *vs, int w, int h)
     if (vs->clientds.pf.bytes_per_pixel == 4) {
         if (vs->tight.pixel24) {
             errors = tight_detect_smooth_image24(vs, w, h);
-            if (vs->tight.quality != -1) {
+            if (vs->tight.quality != (uint8_t)-1) {
                 return (errors < tight_conf[quality].jpeg_threshold24);
             }
             return (errors < tight_conf[compression].gradient_threshold24);
@@ -443,7 +443,7 @@ static int tight_fill_palette(VncState *vs, int x, int y,
              * Should never happen, but don't break everything          \
              * if it does, use the first color instead                  \
              */                                                         \
-            if (idx == -1) {                                            \
+            if (idx == (uint8_t)-1) {                                   \
                 idx = 0;                                                \
             }                                                           \
             while (rep >= 0) {                                          \