drm/msm/sde: fix blob memory leak during mode set

During mode set, new blobs are created but previous
blobs are not copied into the connector. Hence on
every set blob data, previous blobs are not freed
resulting in leak. Fix to update the connector
blob info structure with previous blob.

Change-Id: Ib168e7e3148d23f6cdbf7e1cec2b17d2e139a07d
Signed-off-by: Jayant Shekhar <jshekhar@codeaurora.org>