Make the local variables and functions static. Some of them are not exported by their
symbol name but used trough other means. For example a pointer of the operation
structure is passed through a function call.

This will remove the following sparse warnings (see "make C=1"):
 * pd-video.c:20:5: warning: symbol 'usb_transfer_mode' was not declared. Should it be static?
 * pd-video.c:621:5: warning: symbol 'fire_all_urb' was not declared. Should it be static?
 * pd-video.c:881:5: warning: symbol 'vidioc_s_std' was not declared. Should it be static?
 * pd-video.c:1024:5: warning: symbol 'vidioc_g_audio' was not declared. Should it be static?
 * pd-video.c:1033:5: warning: symbol 'vidioc_s_audio' was not declared. Should it be static?
 * pd-video.c:1193:5: warning: symbol 'usb_transfer_stop' was not declared. Should it be static?
 * pd-video.c:1522:14: warning: symbol 'pd_video_poll' was not declared. Should it be static?
 * pd-video.c:1528:9: warning: symbol 'pd_video_read' was not declared. Should it be static?
 * pd-radio.c:164:5: warning: symbol 'tlg_fm_vidioc_g_tuner' was not declared. Should it be static?
 * pd-radio.c:206:5: warning: symbol 'fm_get_freq' was not declared. Should it be static?
 * pd-radio.c:249:5: warning: symbol 'fm_set_freq' was not declared. Should it be static?
 * pd-radio.c:261:5: warning: symbol 'tlg_fm_vidioc_g_ctrl' was not declared. Should it be static?
 * pd-radio.c:267:5: warning: symbol 'tlg_fm_vidioc_g_exts_ctrl' was not declared. Should it be static?
 * pd-radio.c:288:5: warning: symbol 'tlg_fm_vidioc_s_exts_ctrl' was not declared. Should it be static?
 * pd-radio.c:315:5: warning: symbol 'tlg_fm_vidioc_s_ctrl' was not declared. Should it be static?
 * pd-radio.c:321:5: warning: symbol 'tlg_fm_vidioc_queryctrl' was not declared. Should it be static?
 * pd-radio.c:340:5: warning: symbol 'tlg_fm_vidioc_querymenu' was not declared. Should it be static?
 * pd-main.c:58:12: warning: symbol 'firmware_name' was not declared. Should it be static?
 * pd-main.c:59:19: warning: symbol 'poseidon_driver' was not declared. Should it be static?
Signed-off-by: Márton Németh <nm127@freemail.hu>
Acked-by: Huang Shijie <shijie8@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>