serial: msm_geni_serial: Check if port is open in msm_geni_wakeup_work

msm_geni_wakeup_work is waiting WAKEBYTE_TIMEOUT_MSEC for
wakeup_byte to receive. During this time period shutdown
was called and tty port is closed. Due to timeout
msm_geni_wakeup_work is calling msm_geni_serial_power_off
which registered for wakeup_isr while tty_struct is NULL.
In wakeup_isr excessive warnings got printed since
tty_struct is NULL resulting in watchdog bark.

Upon timeout in msm_geni_wakeup_isr check if tty port
is open else return, which prevents calling of
msm_geni_serial_power_off when tty_struct is NULL.

Change-Id: I0a703620b04ed0eae11452cde90f2456fce8b43b
Signed-off-by: Visweswara Tanuku <quic_vtanuku@quicinc.com>
Signed-off-by: Panicker Harish <quic_pharish@quicinc.com>