On particularly weak signals, changing register 0xab after setting the
interleave mode will cause the FEC lock to get lost (while still holding the
EQ lock).  So remove the write entirely, which seems to have had no adverse
effect in either of my ClearQAM environments (and in particular resolves the
customer's reported issue).

Also flip around the order of the amhum optimization and the interleave setup
to be consistent with the windows driver, which has the side-benefit of doing
them both in the same call (since the amhum optimization can only be done once
the interleave setup).

This work was sponsored by ONELAN Limited.
Signed-off-by: Devin Heitmueller <dheitmueller@kernellabs.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>