video: tegra: avoid null deref on nvdps read

When reading nvdps sysfs file, check mode to avoid a null dereference.

Bug 1032235
Bug 1283024

Change-Id: I19b3b5b3de6743cdcc9e3a846a4ba102de681ad3
Signed-off-by: Haley Teng <hteng@nvidia.com>
arm:tegra:enrc2b: Increase MC_EMEM_ARB_OUTSTANDING_REQ to resolve underflow in low emc freq.
New outstanding request is updated in the emc dvfs table:
* 25.5Mhz: 20
* 51Mhz: 20
* 102Mhz: 30

Bug 1057414

Change-Id: I4d72b0db586ad99d6a6758737d87b3f68e6a47c4
Signed-off-by: Haley Teng <hteng@nvidia.com>