media: tuners: Constify struct tunertype, tuner_range and tuner_params

'struct tunertype', 'struct tuner_range' and 'struct tuner_params' are not
modified in this driver.

Constifying these structures moves some data to a read-only section, so
increase overall security.

On a x86_64, with allmodconfig:
Before:
======
   2877	   8554	      0	  11431	   2ca7	drivers/media/tuners/tuner-types.o

After:
=====
   text	   data	    bss	    dec	    hex	filename
  11421	     48	      0	  11469	   2ccd	drivers/media/tuners/tuner-types.o

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>