msm_serial_hs: Add check to validate wakeup irq in UART clock on request

Wakeup irq is UART RX GPIO IRQ line to be configured as wakeup source and
is used as an optional property with UART. By default wakeup irq is set as
zero when it is not to be used with UART.
During UART clock on request msm_hs_request_clock_on(), calling
disable_irq_nosync() without validating wakeup irq is causing warning
message.
Hence fixing the issue by adding check to validate the wakeup irq during
UART clock on request.

CRs-Fixed: 490597
Change-Id: Iff014f41428d590117e469c1b470736383a78848
Signed-off-by: Saket Saurabh <ssaurabh@codeaurora.org>