msm: mdss: remove unused register read request and invalid comment

Ctl rev in vfp update method is unused. Remove this nop
instruction. DSI timing mode configuration is not specific for
8916/8939 target but common for all targets. Remove such
invalid target specific comment.

Change-Id: Ie7c75203ca50e6bd2abf952f4d4362314c01987c
Signed-off-by: Dhaval Patel <pdhaval@codeaurora.org>