mmc: atmel-mci: Simplify if(chan) and if(!chan)

Use if(!host->dma.chan) instead of if(chan) and if(!chan) to make
code better.

Signed-off-by: Wan Jiabing <wanjiabing@vivo.com>
Link: https://lore.kernel.org/r/20220427120310.838843-1-wanjiabing@vivo.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>