MLK-11848-2 dma: imx-sdma: add __init for probe()

Fix buiding error with GCC 4.6.2:

WARNING: drivers/dma/built-in.o(.text+0xefac): Section mismatch in reference from the function sdma_probe() to the function .init.text:sdma_event_remap.isra.21()
The function sdma_probe() references
the function __init sdma_event_remap.isra.21().
This is often because sdma_probe lacks a __init
annotation or the annotation of sdma_event_remap.isra.21 is wrong.

Signed-off-by: Robin Gong <b38343@freescale.com>