staging: bcm2835-camera: Avoid unneeded internal declaration warning

Clang warns:

drivers/staging/vc04_services/bcm2835-camera/controls.c:59:18: warning:
variable 'mains_freq_qmenu' is not needed and will not be emitted
[-Wunneeded-internal-declaration]
static const s64 mains_freq_qmenu[] = {
                 ^
1 warning generated.

This is because mains_freq_qmenu is currently only used in an ARRAY_SIZE
macro, which is a compile time evaluation in this case. Avoid this by
adding mains_freq_qmenu as the imenu member of this structure, which
matches all other controls that uses the ARRAY_SIZE macro in v4l2_ctrls.
This turns out to be a no-op because V4L2_CID_MPEG_VIDEO_BITRATE_MODE is
defined as a MMAL_CONTROL_TYPE_STD_MENU, which does not pass the imenu
definition along to v4l2_ctrl_new in bm2835_mmal_init_controls.

Link: https://github.com/ClangBuiltLinux/linux/issues/122
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/vc04_services/bcm2835-camera/controls.c

@@ -1106,7 +1106,7 @@ static const struct bm2835_mmal_v4l2_ctrl v4l2_ctrls[V4L2_CTRL_COUNT] = {
 	{
 		V4L2_CID_POWER_LINE_FREQUENCY, MMAL_CONTROL_TYPE_STD_MENU,
 		0, ARRAY_SIZE(mains_freq_qmenu) - 1,
-		1, 1, NULL,
+		1, 1, mains_freq_qmenu,
 		MMAL_PARAMETER_FLICKER_AVOID,
 		&ctrl_set_flicker_avoidance,
 		false