ARM: sa1111: fix error code propagation in sa1111_probe()

Ensure that we propagate the platform_get_irq() error code out of the
probe function.  This allows probe deferrals to work correctly should
platform_get_irq() not be able to resolve the interrupt in a DT
environment at probe time.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>