staging: et131x: Remove incorrect comments regarding alignment

A previous change removed code that aligned memory returned from
dma_alloc_coherent() to a 4k boundary, which was not necessary.

Some comments regarding this alignment still exist, so remove them
as they no longer apply.

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