tty: serial: qcom_geni_serial: IRQ cleanup

Move ISR registration from startup to probe function to avoid registering
it everytime when the port open is called for driver.

Signed-off-by: Akash Asthana <akashast@codeaurora.org>
Link: https://lore.kernel.org/r/1570700763-17319-1-git-send-email-akashast@codeaurora.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>