msm: camera: Initialize the vb2 queue during buffer registration.

Move the vb2 queue initialization from set_format to
reqbuf(buffer registration). This is to ensure that the
user does not have to set the format again, if he is trying
to stop and start a stream.

Change-Id: I902072a33fcf43ed882759c14d327667c42a88bd
Signed-off-by: Kiran Kumar H N <hurlisal@codeaurora.org>