[media] media: s5p-mfc: use vb2_ops_wait_prepare/finish helper

[media] media: s5p-mfc: use vb2_ops_wait_prepare/finish helper

This patch drops driver specific wait_prepare() and
wait_finish() callbacks from vb2_ops and instead uses
the the helpers vb2_ops_wait_prepare/finish() provided
by the vb2 core, the lock member of the queue needs
to be initalized to a mutex so that vb2 helpers
vb2_ops_wait_prepare/finish() can make use of it.

Signed-off-by: Lad, Prabhakar <[email protected]>
Cc: Kyungmin Park <[email protected]>
Cc: Kamil Debski <[email protected]>
Cc: Jeongtae Park <[email protected]>
Signed-off-by: Kamil Debski <[email protected]>
Signed-off-by: Mauro Carvalho Chehab <[email protected]>