Btrfs-progs: fix check to test trim support

It was added in 25d82d22 but broke recently in 4724d7b0 while making
discard interruptible.

Signed-off-by: Rakesh Pandit <rakesh@tuxera.com>
Signed-off-by: David Sterba <dsterba@suse.cz>

utils.c

@@ -626,7 +626,7 @@ int btrfs_prepare_device(int fd, char *file, int zero_end, u64 *block_count_ret,
 		 * is not necessary for the mkfs functionality but just an
 		 * optimization.
 		 */
-		if (discard_blocks(fd, 0, 0) == 0) {
+		if (discard_range(fd, 0, 0) == 0) {
 			fprintf(stderr, "Performing full device TRIM (%s) ...\n",
 				pretty_size(block_count));
 			discard_blocks(fd, 0, block_count);