media: verisilicon: Do not use ctx fields as format storage when resetting

Source and destination pixel formats fields of context structure should
not be used as storage when resetting the format.
Use local variables instead and let hantro_set_fmt_out() and
hantro_set_fmt_cap() set them correctly later.

Signed-off-by: Benjamin Gaignard <benjamin.gaignard@collabora.com>
Reviewed-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>