loop: fix type of block size

loop: fix type of block size

PAGE_SIZE may be 64K, and the max block size can be PAGE_SIZE, so any
variable for holding block size can't be defined as 'unsigned short'.

Unfortunately commit 473516b36193 ("loop: use the atomic queue limits
update API") passes 'bsize' with type of 'unsigned short' to
loop_reconfigure_limits(), and causes LTP/ioctl_loop06 test failure:

  12 ioctl_loop06.c:76: TINFO: Using LOOP_SET_BLOCK_SIZE with arg > PAGE_SIZE
  13 ioctl_loop06.c:59: TFAIL: Set block size succeed unexpectedly
  ...
  18 ioctl_loop06.c:76: TINFO: Using LOOP_CONFIGURE with block_size > PAGE_SIZE
  19 ioctl_loop06.c:59: TFAIL: Set block size succeed unexpectedly

Fixes the issue by defining 'block size' variable with 'unsigned int', which is
aligned with block layer's definition.

(improve commit log & add fixes tag)

Fixes: 473516b36193 ("loop: use the atomic queue limits update API")
Cc: John Garry <john.g.garry@oracle.com>
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Jan Stancek <jstancek@redhat.com>
Signed-off-by: Li Wang <liwang@redhat.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: John Garry <john.g.garry@oracle.com>
Link: https://lore.kernel.org/r/20241109022744.1126003-1-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>