staging: vt6656: Use const for read only data

Use const for the arrays that are used as "read only". Also, modify the
prototype of vnt_control_out_blocks() function to use a pointer to a
const type.

The vnt_vt3184_al2230 array can't be converted to const as it's modified
later.

Then in the vnt_vt3184_init() function use two types of pointers (to
const type and to no const type) to avoid the compiler warning:

assignment discards 'const' qualifiers from pointer target type

This way decrease the .data section and increase the .rodata section
limiting the surface attack.

Before this change:
-------------------

drivers/staging/vt6656/baseband.o  :
section              size   addr
.text                1278      0
.data                 576      0
.bss                    0      0
.rodata               319      0
.comment               45      0
.note.GNU-stack         0      0
.note.gnu.property     32      0
Total                2250

After this change:
------------------

drivers/staging/vt6656/baseband.o  :
section              size   addr
.text                1278      0
.data                 256      0
.bss                    0      0
.rodata               640      0
.comment               45      0
.note.GNU-stack         0      0
.note.gnu.property     32      0
Total                2251

Signed-off-by: Oscar Carter <oscar.carter@gmx.com>
Link: https://lore.kernel.org/r/20200504171414.11307-1-oscar.carter@gmx.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>