media: usbtv: Keep norm parameter specific

The user-supplied norm value gets overwritten by the generic .norm
member from the norm_params. That way, we lose the specific norm the
user may want to set.

For instance, if the user specifies V4L2_STD_PAL_60, the value actually
used will be V4L2_STD_525_60, which in the end will be as if the user
had specified V4L2_STD_NTSC, since this is always the first bitfield we
match the norm value against before configuring the hardware.

The norm_params array is only there to match a norm with an output
resolution. The norm value itself should not be changed.

Signed-off-by: Hugo Grostabussiat <bonstra@bonstra.fr.eu.org>
Signed-off-by: Hans Verkuil <hansverk@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>