byte-cntr: Don't write csr register when byte-cntr is disabled

It is possible that byte-cntr release happens after byte-cntr is disabled.
Don't write csr register when byte-cntr is disabled to avoid the register
access issue.

Change-Id: Ic818107e1bcbe31e1a55cdc8c0f6ff89ff70564f
Signed-off-by: Mao Jinlong <jinlmao@codeaurora.org>