scsi: ufs: remove byte count duplication in long sequential tests

The test byte count is incremented in the test-iosched framework code,
and in the ufs_long_sequential test it is again incremented.
This leads to a double amount of bytes "transferred" and therefore to
a double calculated throughput.
This patch removes the duplicate incrementation of the byte count.

Change-Id: Ieeddd7379d6e641400108892f27fc8f81ec7f245
Signed-off-by: Lee Susman <lsusman@codeaurora.org>