dmaengine: imx-sdma: remove dummy assignment

David reported:
drivers/dma/imx-sdma.c:1003]: (style) Same expression on both sides of '|='

ORing with itself yields same result, So remove this

Reported-by: David Binderman <dcb314@hotmail.com>
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Cc: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>