scsi: ufs: fix sector increment in ufs_long_seq_test

Currently, request sector is incremented in the long sequential test
using a calculation which assumes the device logical block size is
512B (equal to sector size) but this is not the case.
This patch changes the calculation to be correct, using the test bio size,
and assuming sector size is 512B.

Change-Id: I807be243b65834edf9201488a849777e43bb658a
Signed-off-by: Lee Susman <lsusman@codeaurora.org>
Signed-off-by: Yaniv Gardi <ygardi@codeaurora.org>