V4L/DVB (11685): gspca - gspca-m5602: Constify parameters of two functions

A number of parameters to some functions in the m5602 are constant and should be flagged as such.

Signed-off-by: Erik Andrén <erik.andren@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>