net: dsa: microchip: simplify ksz_prmw8()

Implement ksz_prmw8() in terms of ksz_rmw8(), just as all the other
ksz_pX are implemented in terms of ksz_X. No functional change.

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Acked-by: Arun Ramadoss <arun.ramadoss@microchip.com>
Link: https://lore.kernel.org/r/20230620113855.733526-2-linux@rasmusvillemoes.dk


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