serial: msm_geni_serial: Do not drop port->lock in polling mode

In issue case process x already locked uport->lock, whereas process y
trying to unlock same lock. This is resulting in invalid owner spin_bug.

To fix this issue added changes in driver to unlock and lock only
for the interrupt context.

Change-Id: Ifb174a11fc8dce111d0ee7c8bf3efd0e56d084f6
Signed-off-by: Chandana Kishori Chiluveru <cchiluve@codeaurora.org>