msm: mdss: fix memcpy source and dest memory buffer size mismatch

Currently memcpy is copying from a bigger memory size to a smaller
memory size. This change corrects this issue by performing the
memcopy restricted to the smaller of the src or dest memory buffer.

Change-Id: Ibbe5665083799a4262d3cfbb06f94f3e35e03748
Signed-off-by: Harsh Sahu <hsahu@codeaurora.org>