msm-geni-serial: Correct the interrupt polling logic in uart

Correct the interrupt polling logic in uart and depend on the
interrupt routine instead of polling where ever possible.

Change-Id: Ia01889549d7edbe380e2e58b92efb2a0b3b34e7b
Signed-off-by: Prudhvi Yarlagadda <pyarlaga@codeaurora.org>