media: vicodec: bugfix - replace '=' with '|='

In the fwht_encode_frame, 'encoding = encode_plane'
should be replaced with 'encoding |= encode_plane'
so existing flags won't be overwrriten.

Signed-off-by: Dafna Hirschfeld <dafna3@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>