bayer: fix stride inconsistencies for odd widths

bayer: fix stride inconsistencies for odd widths

Consistently use GST_ROUND_UP_4(width) as stride for
bayer buffers. Bayer data will usually come in widths
that are multiples of 4 anyway, so hopefully this
should not have any adverse impact on anyone in
practice.

Before, bayer2rgb required input buffers to are sized
accordingly, but then didn't actually round up when
calculating row offsets. rgb2bayer didn't use a rounded
stride nor buffer size.

https://bugzilla.gnome.org/show_bug.cgi?id=752014