drivers: uart: initialize spin_lock before use

In linux guest restart case, during probe, stop_rx_sequencer is
getting called because of residual state set before restart.

spin_lock which is used in stop_rx_sequencer is not initialized.
To, resolve spin_lock debug mentioned below, initialize spin_lock
early.

		spin_dump+0x84/0x88
		do_raw_spin_lock+0xd4/0x12c
		raw_spin_lock+0x20/0x2c
		handle_rx_dma_xfer+0x44/0x330
		stop_rx_sequencer+0x118/0x420
		start_rx_sequencer+0xc0/0x1a0
		msm_geni_serial_runtime_resume+0x54/0xb8
		pm_generic_runtime_resume+0x44/0x80
		__rpm_callback+0x98/0x208
		rpm_resume+0x458/0x6a4
		__pm_runtime_resume+0x60/0xa0
		__device_attach.llvm.18035772682363603059+0xa0/0x174
		bus_probe_device+0x3c/0xdc
		device_add+0x95c/0xb84
		serdev_controller_add_platform+0x2c/0x1d0
		serdev_tty_port_register+0xf8/0x188
		tty_port_register_device_attr_serdev+0x50/0x90
		uart_add_one_port+0x268/0x60c
		msm_geni_serial_probe+0x630/0x780
		platform_drv_probe+0xac/0xf0
		really_probe+0x210/0x7d8.

Change-Id: I9e139897681ece174a9ead63f57bb999585ff0bf
Signed-off-by: Venkata Rao Kakani <vkakani@codeaurora.org>