zram: allow request end to coincide with disksize

(cherry pick from commit 75c7caf5a052ffd8db3312fa7864ee2d142890c4)

Pass valid_io_request() checks if request end coincides with disksize
(end equals bound), only fail if we attempt to read beyond the bound.

mkfs.ext2 produces numerous errors:
[ 2164.632747] quiet_error: 1 callbacks suppressed
[ 2164.633260] Buffer I/O error on device zram0, logical block 153599
[ 2164.633265] lost page write due to I/O error on zram0

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Bug: 24810447
Change-Id: I9e909fa82a3b2a9c42e4396788b6121204e471e2