Cleanup using bitrev8 in cm4000_cs driver.

Cc: Harald Welte <laforge@gnumonks.org>
Signed-off-by: NAkinobu Mita <akinobu.mita@gmail.com>
Cc: Dominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>