Input: atmel_mxt_ts - fix -Wunused-const-variable

Clang produces the following warning

drivers/input/touchscreen/atmel_mxt_ts.c:259:42: warning: unused
variable 'mxt_video_fops' [-Wunused-const-variable]
static const struct v4l2_file_operations mxt_video_fops = {

Since mxt_video_fops is only used inside an ifdef. It should
be moved inside the ifdef.

Link: https://github.com/ClangBuiltLinux/linux/issues/527


Signed-off-by: Nathan Huckleberry <nhuck@google.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>