Make strtosz() return int64_t instead of ssize_t

strtosz() needs to return a 64 bit type even on 32 bit
architectures. Otherwise qemu-img will fail to create disk
images >= 2GB

Signed-off-by: Jes Sorensen <Jes.Sorensen@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
diff --git a/monitor.c b/monitor.c
index d291158..0cda3da 100644
--- a/monitor.c
+++ b/monitor.c
@@ -4162,7 +4162,7 @@
             break;
         case 'o':
             {
-                ssize_t val;
+                int64_t val;
                 char *end;
 
                 while (qemu_isspace(*p)) {