dmaengine: axi-dmac: Propagate errors from platform_get_irq()

Propagate errors returned by platform_get_irq() to the driver core. This
will enable proper probe deferring for the driver in case the IRQ provider
has not been registered yet.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>