dmaengine: make mux_configure32 static

dmaengine: make mux_configure32 static

There is one sparse warning in drivers/dma/fsl-edma-common.c:
drivers/dma/fsl-edma-common.c:93:6: warning: symbol 'mux_configure32'
was not declared. Should it be static?

Fix it by setting mux_configure32() as static.

Fixes: 232a7f18cf8ec ("dmaengine: fsl-edma: add i.mx7ulp edma2 version support")
Signed-off-by: Mao Wenan <maowenan@huawei.com>
Link: https://lore.kernel.org/r/20190814072105.144107-2-maowenan@huawei.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>