scsi: ufs: fix's to ufs_parallel test

This patch fixes the ufs unit test case "parallel_read_write_test"
to work properly. Changes are mainly in the logic deciding on the toggle
of request direction.

Change-Id: I3ba60421de1afb05dca780d82fcf10b9910a0bc1
Signed-off-by: Lee Susman <lsusman@codeaurora.org>