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/qemu-img.c b/qemu-img.c
index 1e65ea8..4a37358 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -320,7 +320,7 @@
 
     /* Get image size, if specified */
     if (optind < argc) {
-        ssize_t sval;
+        int64_t sval;
         sval = strtosz_suffix(argv[optind++], NULL, STRTOSZ_DEFSUFFIX_B);
         if (sval < 0) {
             error_report("Invalid image size specified! You may use k, M, G or "