ide: fix enum comparison for gcc 4.7

Apparently GCC gets bent over comparing enum values against zero.
Replace the conditional with something less readable.
Tested-by: NMark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Signed-off-by: NJohn Snow <jsnow@redhat.com>
Reviewed-by: NStefan Hajnoczi <stefanha@redhat.com>
Message-id: 20170921013821.1673-1-jsnow@redhat.com
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

hw/ide/ahci.c

@@ -184,7 +184,7 @@ static void ahci_check_irq(AHCIState *s)
 static void ahci_trigger_irq(AHCIState *s, AHCIDevice *d,
                              enum AHCIPortIRQ irqbit)
 {
-    g_assert(irqbit >= 0 && irqbit < 32);
+    g_assert((unsigned)irqbit < 32);
     uint32_t irq = 1U << irqbit;
     uint32_t irqstat = d->port_regs.irq_stat | irq;
 

hw/ide/core.c

@@ -68,7 +68,7 @@ const char *IDE_DMA_CMD_lookup[IDE_DMA__COUNT] = {
 
 static const char *IDE_DMA_CMD_str(enum ide_dma_cmd enval)
 {
-    if (enval >= IDE_DMA__BEGIN && enval < IDE_DMA__COUNT) {
+    if ((unsigned)enval < IDE_DMA__COUNT) {
         return IDE_DMA_CMD_lookup[enval];
     }
     return "DMA UNKNOWN CMD";

include/hw/ide/internal.h

@@ -333,8 +333,7 @@ struct unreported_events {
 };
 
 enum ide_dma_cmd {
-    IDE_DMA__BEGIN = 0,
-    IDE_DMA_READ = IDE_DMA__BEGIN,
+    IDE_DMA_READ = 0,
     IDE_DMA_WRITE,
     IDE_DMA_TRIM,
     IDE_DMA_ATAPI,