serial: msm_geni_serial: Remove remaining power votes at shutdown

If during port shutdown, there are any remaining ioctl votes, then remove
these votes.
Ideally we want clients to remove the resource votes they put in, but if
the client userspace is forcefully terminated then they may not get a
chance to vote these off. Under such situations, the driver can remove any
remaining resource votes as leaving them around will prevent the device
from entering low power modes.

Change-Id: I46d054de97361e9a077f12b20373ba80f029a720
Signed-off-by: Girish Mahadevan <girishm@codeaurora.org>