dmaengine i.MX SDMA: Fix firmware loading

When loading the microcode to the SDMA engine we have to use
the ram_code_start_addr found in the firmware image. The copy
in the sdma engine is not initialized correctly. This is broken
since:
5b28aa31 dmaengine i.MX SDMA: Allow to run without firmware

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>