msm: vidc_3x: correct ion flags for CP_CAMERA_ENCODE context bank

if CP_CAMERA_ENCODE context bank enabled, ION_FLAG_CP_PIXEL ion flag
should be replaced with  ION_FLAG_CP_CAMERA_ENCODE, otherwise mapping
would fail.

Change-Id: I142042f0d8da143e514d5862febac82885761ad9
Signed-off-by: Srinu Gorle <sgorle@codeaurora.org>