kvm: Fix enable_cap helpers on older gcc

Commit 40f1ee27 introduced handy helpers for enable_cap calls on
vcpu and vm level. Unfortunately some older gcc versions (4.7.1, 4.6)
seem to choke on signedness detection in inline created variables:

target-ppc/kvm.c: In function 'kvmppc_booke_watchdog_enable':
target-ppc/kvm.c:1302:21: error: comparison of unsigned expression < 0 is always false [-Werror=type-limits]
target-ppc/kvm.c: In function 'kvmppc_set_papr':
target-ppc/kvm.c:1504:21: error: comparison of unsigned expression < 0 is always false [-Werror=type-limits]

However - thanks to Thomas Huth for the suggestion - we can just cast the
offending potentially 0 value to a signed type, making the comparison signed.
Reviewed-by: NThomas Huth <thuth@linux.vnet.ibm.com>
Acked-by: NCornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: NAlexander Graf <agraf@suse.de>
Signed-off-by: NCornelia Huck <cornelia.huck@de.ibm.com>

include/sysemu/kvm.h

@@ -300,7 +300,7 @@ int kvm_check_extension(KVMState *s, unsigned int extension);
         };                                                           \
         uint64_t args_tmp[] = { __VA_ARGS__ };                       \
         int i;                                                       \
-        for (i = 0; i < ARRAY_SIZE(args_tmp) &&                      \
+        for (i = 0; i < (int)ARRAY_SIZE(args_tmp) &&                 \
                      i < ARRAY_SIZE(cap.args); i++) {                \
             cap.args[i] = args_tmp[i];                               \
         }                                                            \
@@ -315,7 +315,7 @@ int kvm_check_extension(KVMState *s, unsigned int extension);
         };                                                           \
         uint64_t args_tmp[] = { __VA_ARGS__ };                       \
         int i;                                                       \
-        for (i = 0; i < ARRAY_SIZE(args_tmp) &&                      \
+        for (i = 0; i < (int)ARRAY_SIZE(args_tmp) &&                 \
                      i < ARRAY_SIZE(cap.args); i++) {                \
             cap.args[i] = args_tmp[i];                               \
         }                                                            \