bio: fix argument of __bio_add_page() for max_sectors > 0xffff

The data type of max_sectors and max_hw_sectors in queue settings are
unsigned int.  But these values are passed to __bio_add_page() as an
argument whose data type is unsigned short.  In the worst case such as
max_sectors is 0x10000, bio_add_page() can't add a page and IOs can't
proceed.

Cc: Jens Axboe <axboe@kernel.dk>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>