[media] au0828-cards: remove a comment about i2c clock stretching

This comment is already at the au0828-i2c where it belongs.
So, remove it from a board's entry. It doesn't make any sense
there, as we're setting the clock to 250kHz there, slowing it
down only at the au0828-i2c.

Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>