staging: et131x: Remove frame error TODO item

After prolonged testing for a few days of normal use with new et131x
hardware, I've concluded that this was a hardware issue with the older
hardware I had. Removing this item from the TODO.

Signed-off-by: Mark Einon <mark.einon@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>