msm: vidc: Search for buffer using buffer address

Instead of using clnt_data, which is a cookie passed
through firmware, use buffers device address to search
for corresponding video buffer header.

Change-Id: I2f168ac58dbbdfc698b35afb0ebaddde6c9fa6e3
Signed-off-by: Vinay Kalia <vkalia@codeaurora.org>