media: rtl28xxu: make array rc_nec_tab static const

Don't populate the array rc_nec_tab on the stack, instead make it
static const. Makes the object code smaller by over 620 bytes:

Before:
   text	   data	    bss	    dec	    hex	filename
  49511	  17040	     64	  66615	  10437	rtl28xxu.o

After:
   text	   data	    bss	    dec	    hex	filename
  48825	  17104	     64	  65993	  101c9	rtl28xxu.o

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Hans Verkuil <hansverk@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>