net: ethernet: renesas: rcar_gen4_ptp: Remove incorrect comment

The comments intent was to indicates which function uses the enum. While
upstreaming rcar_gen4_ptp the function was renamed but this comment was
left with the old function name.

Instead of correcting the comment remove it, it adds little value.

Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>