target-moxie: Fix warnings from Sparse (one-bit signed bitfield)

Report from Sparse:

target-moxie/mmu.h:9:12: error: dubious one-bit signed bitfield
target-moxie/mmu.h:10:12: error: dubious one-bit signed bitfield
target-moxie/mmu.h:11:12: error: dubious one-bit signed bitfield
target-moxie/mmu.h:12:12: error: dubious one-bit signed bitfield
target-moxie/mmu.h:13:12: error: dubious one-bit signed bitfield

Cc: Anthony Green <green@moxielogic.com>
Signed-off-by: NStefan Weil <sw@weilnetz.de>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

target-moxie/mmu.h

@@ -6,11 +6,11 @@
 typedef struct {
     uint32_t phy;
     uint32_t pfn;
-    int g:1;
-    int v:1;
-    int k:1;
-    int w:1;
-    int e:1;
+    unsigned g:1;
+    unsigned v:1;
+    unsigned k:1;
+    unsigned w:1;
+    unsigned e:1;
     int cause_op;
 } MoxieMMUResult;