media: vsp1: use periods at the end of comment sentences

The style of this driver uses periods at the end of sentences in
comments, but it is applied inconsitently.

Update a selection of comments which were discovered to be missing their
period. Also fix the spelling of one usage of 'instantiate'

Signed-off-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>