media: aspeed: fix mode-detect always time out at 2nd run

aspeed_video_get_resolution() will try to do res-detect again if the
timing got in last try is invalid. But it will always time out because
VE_SEQ_CTRL_TRIG_MODE_DET is only cleared after 1st mode-detect.

To fix the problem, just clear VE_SEQ_CTRL_TRIG_MODE_DET before setting
it in aspeed_video_enable_mode_detect().

Fixes: d2b4387f ("media: platform: Add Aspeed Video Engine driver")
Signed-off-by: Jammy Huang <jammy_huang@aspeedtech.com>
Acked-by: Paul Menzel <pmenzel@molgen.mpg.de>
Reviewed-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>