media: rp1: fe: Fix default mbus code

When pisp_fe_pad_set_fmt() is given an mbus code that CFE does not
support, it currently defaults to MEDIA_BUS_FMT_SBGGR10_1X10. This is
not correct, as FE does not support SBGGR10.

Set the default to MEDIA_BUS_FMT_SRGGB16_1X16 instead.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>