msm: mdss: validate number of cea blocks before reading from edid_buf

Number of cea blocks are read from edid buffer which comes from the
user. If the number of cea blocks are more than the supported blocks
kernel information leak is possible by reading more data than is
present in edid_buf.

Change-Id: I03b8456ff1e1a7b15d711f06908bd5c83f83cc02
Signed-off-by: Ashish Garg <ashigarg@codeaurora.org>