serial: xilinx: Use platform_get_irq to get irq description structure

commit 5c90c07b98c02198d9777a7c4f3047b0a94bf7ed upstream.

For systems with CONFIG_SERIAL_OF_PLATFORM=y and device_type =
"serial"; property in DT of_serial.c driver maps and unmaps IRQ (because
driver probe fails). Then a driver is called but irq mapping is not
created that's why driver is failing again in again on request_irq().
Based on this use platform_get_irq() instead of platform_get_resource()
which is doing irq_desc allocation and driver itself can request IRQ.

Fix both xilinx serial drivers in the tree.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[bwh: Backported to 3.2:
 - Adjust context
 - Return directly on failure in xuartps_probe()]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --cc drivers/tty/serial/uartlite.c
Simple merge

diff --cc drivers/tty/serial/xilinx_uartps.c
Simple merge