msm: camera: Get the buffer manger subdev using msm_sd_find

Instead of getting the buffer manger subdev by
directly calling buffer manger api use the
msm_sd_find to get it.

Change-Id: I8392f5eabcfc3900b124415411a8b035e410603a
Signed-off-by: Hariram Purushothaman <hariramp@codeaurora.org>