tty: serial: qcom_geni_serial: Fix UART hang

If a serial console write occurred while a UART transmit command was
waiting for a done signal then no further data would be sent until
something new kicked the system into gear. If there is already data
waiting in the circular buffer we must re-enable the tx watermark so we
receive the expected interrupts.

Change-Id: I89ae1c21942350dea25052ba9dea9080778f6d79
Signed-off-by: Ryan Case <ryandcase@chromium.org>
Git-commit: 663abb1a7a7ff8fea9ab0145463de7fcff823755
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


[msavaliy@codeaurora.org: Applied patch to downstream file - msm_geni_serial.c]
Signed-off-by: Mukesh Kumar Savaliya <msavaliy@codeaurora.org>