net: qede: fix kernel-doc for qede_ptp_adjfreq()

One of the function arguments was renamed some time ago, but this
wasn't reflected in its kernel-doc comment.
Also add the description for return values.

Signed-off-by: Alexander Lobakin <alobakin@marvell.com>
Signed-off-by: Igor Russkikh <irusskikh@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>