qemu-io: Fix return value handling of bdrv_open

bdrv_open may return -errno so we have to check
if the return value is '< 0', not '== -1'.
Signed-off-by: NRyota Ozaki <ozaki.ryota@gmail.com>
Signed-off-by: NAurelien Jarno <aurelien@aurel32.net>

qemu-io.c

@@ -1284,7 +1284,7 @@ static int openfile(char *name, int flags, int growable)
 		flags |= BDRV_O_FILE;
 	}
 
-	if (bdrv_open(bs, name, flags) == -1) {
+	if (bdrv_open(bs, name, flags) < 0) {
 		fprintf(stderr, "%s: can't open device %s\n", progname, name);
 		bs = NULL;
 		return 1;