msm_serial_hs: Vote for clocks during tty close

While BT operation is in progress, it's possible for
client functions to explicitly turn off the
UART clocks without notifying TTY layer.  Then when
TTY layer try to access UART, L2 error happened because
of un-clocked registers.  Since there is no clear way
to notify clients to turn on clocks before TTY access
UART driver will implicilty turn on the clocks.

CRs-Fixed: 505225
Change-Id: Ia9958658465a6c0e5af66cd932e8e694cc12b78c
Signed-off-by: Naveen Kaje <nkaje@codeaurora.org>