msm: mdss: size check before writing to edid buffer

To update custom edid through sysfs node, there was no check
on the edid size passed. The user can overwrite the edid buffer.
To prevent buffer overflow, ensure that edid size is validated
with the edid buffer size before writing to the buffer.

Change-Id: I8604ea2d25f3a4985749bd037497d242b0621519
Signed-off-by: Ashish Garg <ashigarg@codeaurora.org>