media: gspca: remove redundant assignment to variable j

Variable j is being set to zero before a loop and also
immediately inside the loop and is not used after the loop.
Hence the first assignment is redundant and can be removed.
Cleans up clang warning:

drivers/media/usb/gspca/gspca.c:1078:2: warning: Value stored
to 'j' is never read

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