net: ethernet: ravb: Remove redundant argument to ravb_ptp_init()

There is no need to explicitly pass the struct platform_device pointer
to ravb_ptp_init(), it can retrieve it directly from the private data
structure.

Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Sergey Shtylyov <sergei.shtylyov@gmail.com>
Link: https://patch.msgid.link/20260921175037.4084310-5-niklas.soderlund+renesas@ragnatech.se
Signed-off-by: Jakub Kicinski <kuba@kernel.org>