media: aspeed: Correct value for h-total-pixels

Previous reg-field, 0x98[11:0], stands for the period of the detected
hsync signal.
Use the correct reg, 0xa0, to get h-total in pixels.

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