net: ethernet: ravb: Propagate error from ptp_clock_register()

If the PTP clock registration failed the error is silently ignored.
Before reworking all callers of ravb_ptp_init() handle and propagate the
error so it can be used.

Link: https://sashiko.dev/#/patchset/20260610102432.3538432-2-niklas.soderlund+renesas@ragnatech.se?part=1
Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Sergey Shtylyov <sergei.shtylyov@gmail.com>
Link: https://patch.msgid.link/20260921175037.4084310-6-niklas.soderlund+renesas@ragnatech.se
Signed-off-by: Jakub Kicinski <kuba@kernel.org>