serial: pch_uart: trivial cleanup by removing the get_msr()

The short get_msr() has some unnecessary code and only used once,
so merge it with its caller to make code cleaner. No functional
change at all.

Signed-off-by: Feng Tang <feng.tang@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>