mmc: atmel-mci: Check pdata for NULL before dereferencing it at DMA config

mmc: atmel-mci: Check pdata for NULL before dereferencing it at DMA config

Orabug: stable_rc4

[ Upstream commit 93c77d2999b09f2084b033ea6489915e0104ad9c ]

Using an at91sam9g20ek development board with DTS configuration may trigger
a kernel panic because of a NULL pointer dereference exception, while
configuring DMA. Let's fix this by adding a check for pdata before
dereferencing it.

Signed-off-by: Brent Taylor <motobud@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
(cherry picked from commit 0db0888f18f37d9ee10e99a7f3e90861b4d525a2)

Signed-off-by: Dan Duval <dan.duval@oracle.com>