net:fec: remove duplicate lines in comment about errata ERR006358

commit 03191656 worked around
errata ERR006358, but comment contains duplicated lines, impairing
the readability.  Remove them.

Signed-off-by: Philippe De Muyter <phdm@macqel.be>
Signed-off-by: David S. Miller <davem@davemloft.net>