V4L/DVB (8195): gspca: Input buffer overwritten in spca561 + cleanup code.

spca561:  Input buffer may be changed on reg write.
(all sd): Cleanup code, 'const' added.

Signed-off-by: Jean-Francois Moine <moinejf@free.fr>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>