btrfs-progs: Fix getopt on arm platforms

There, 'char' is unsigned, so once assigned '-1' from getopt, it gets
the value 255. Then, it compared to '-1' gives false.

Signed-off-by: Lluis Batlle i Rossell <viric@viric.name>

cmds-scrub.c

@@ -1606,7 +1606,7 @@ static int cmd_scrub_status(int argc, char **argv)
 	int i;
 	int print_raw = 0;
 	int do_stats_per_dev = 0;
-	char c;
+	int c;
 	char fsid[37];
 	int fdres = -1;
 	int err = 0;

cmds-send.c

@@ -416,7 +416,7 @@ out:
 int cmd_send_start(int argc, char **argv)
 {
 	char *subvol = NULL;
-	char c;
+	int c;
 	int ret;
 	char *outname = NULL;
 	struct btrfs_send send;