msm_serial_hs: Cleanup regarding usage of clock enable/disable apis

Currently driver uses clock apis (clock_enable()/clock_disable()) before
accessing any UART Core register. Hence remove all usage of clock apis
which is just increasing the refcount of uart clock instead of turning
on/off the uart lock.

Change-Id: Idf39108e40b23eb7f17d55470247b339a7850a5f
Signed-off-by: Mayank Rana <mrana@codeaurora.org>