media: rc: fix lots of documentation warnings

media: rc: fix lots of documentation warnings

Building the driver with gcc 7.2.1 and:
	make ARCH=i386  CF=-D__CHECK_ENDIAN__ CONFIG_DEBUG_SECTION_MISMATCH=y W=1 CHECK='' M=drivers/media

now produces a lot of warnings:
	drivers/media/rc/rc-main.c:278: warning: No description found for parameter 'new_keycode'
	drivers/media/rc/rc-main.c:278: warning: Excess function parameter 'keycode' description in 'ir_update_mapping'
	drivers/media/rc/rc-main.c:387: warning: No description found for parameter 'ke'
	drivers/media/rc/rc-main.c:387: warning: No description found for parameter 'old_keycode'
	drivers/media/rc/rc-main.c:387: warning: Excess function parameter 'scancode' description in 'ir_setkeycode'
	drivers/media/rc/rc-main.c:387: warning: Excess function parameter 'keycode' description in 'ir_setkeycode'
	drivers/media/rc/rc-main.c:433: warning: Excess function parameter 'to' description in 'ir_setkeytable'
	drivers/media/rc/rc-main.c:506: warning: No description found for parameter 'ke'
	drivers/media/rc/rc-main.c:506: warning: Excess function parameter 'scancode' description in 'ir_getkeycode'
	drivers/media/rc/rc-main.c:506: warning: Excess function parameter 'keycode' description in 'ir_getkeycode'
	drivers/media/rc/rc-main.c:634: warning: No description found for parameter 't'
	drivers/media/rc/rc-main.c:634: warning: Excess function parameter 'cookie' description in 'ir_timer_keyup'

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>