loop: Add LOOP_SET_BLOCK_SIZE in compat ioctl

This change adds LOOP_SET_BLOCK_SIZE as one of the supported ioctls
in lo_compat_ioctl. It only takes an unsigned long argument, and
in practice a 32-bit value works fine.
Reviewed-by: NOmar Sandoval <osandov@fb.com>
Signed-off-by: NEvan Green <evgreen@chromium.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

drivers/block/loop.c

@@ -1612,6 +1612,7 @@ static int lo_compat_ioctl(struct block_device *bdev, fmode_t mode,
 		arg = (unsigned long) compat_ptr(arg);
 	case LOOP_SET_FD:
 	case LOOP_CHANGE_FD:
+	case LOOP_SET_BLOCK_SIZE:
 		err = lo_ioctl(bdev, mode, cmd, arg);
 		break;
 	default: