net: dsa: rzn1_a5psw: Make the read-only array offsets static const

Don't populate the read-only array offsets on the stack at run time,
instead make it static const.

Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Tested-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Link: https://patch.msgid.link/20250417161353.490219-1-colin.i.king@gmail.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>