UPSTREAM: block: fix get_max_io_size()

commit e4b469c66f3cbb81c2e94d31123d7bcdf3c1dabd upstream.

A previous commit aligning splits to physical block sizes inadvertently
modified one return case such that that it now returns 0 length splits
when the number of sectors doesn't exceed the physical offset. This
later hits a BUG in bio_split(). Restore the previous working behavior.

Bug: 173583534
Fixes: 9cc5169c ("block: Improve physical block alignment of split
bios")
Reported-by: Eric Deal <eric.deal@wdc.com>
Signed-off-by: Keith Busch <kbusch@kernel.org>
Cc: Bart Van Assche <bvanassche@acm.org>
Cc: stable@vger.kernel.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Bug: 173583534
(cherry picked from commit f09dbec9)
Signed-off-by: Chenggang Wang <wangchenggang@vivo.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: I5f4708059f106b6ded162cbe096e45bae7a7fca4