dma: imx-sdma: remove incorrect __init annotation from sdma_init()

When platform_driver_probe() is not used, sdma_probe() can be called
by bind/unbind via sysfs. In addition, sdma_init() can be called by
sdma_probe(). Thus, __init annotation should be removed from sdma_init(),
Also, this patch fixes section mismatch warning.

WARNING: drivers/dma/built-in.o(.text+0xd6e4): Section mismatch in reference from the function sdma_probe() to the function
.init.text:sdma_init()
The function sdma_probe() references
the function __init sdma_init().
This is often because sdma_probe lacks a __init
annotation or the annotation of sdma_init is wrong.

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>