dma: imx-sdma: fix another incorrect __init annotation

In e34b731f ("dma: imx-sdma: Remove spurious __init annotation on
sdma_probe()"), Mark found an extraneous __init label and fixed it.

However, he missed another one, because now we get this other warning:

WARNING: drivers/dma/imx-sdma.o(.text+0x3bb4): Section mismatch in reference from the function sdma_probe() to the function .init.text:sdma_get_firmware()
The function sdma_probe() references
the function __init sdma_get_firmware().

Same reasoning as the last time, the function may get called at
runtime, so it can't be __init.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>