msm_serial_hs: fix unbalanced clock vote during port close

This change fixes the clock voting logic when the port is closed and
prevents the clock votes from going negative. Clocks are voted for when
the port is being closed and the conditional unvote based on the clock
state will always be true if the earlier vote is not downvoted before
this check is done. This change also protects agains erroneous, unbalanced
client votes, leading to instabilities.

CRs-Fixed: 550668
Change-Id: I391ac69601314757821b3ffb931a00647a64c583
Signed-off-by: Naveen Kaje <nkaje@codeaurora.org>