realtek: pcs: use ARRAY_SIZE kernel macro

realtek: pcs: use ARRAY_SIZE kernel macro

In the RTL931X configuration code, the array size of configuration
arrays was still calculated with 'sizeof(...) / sizeof(...)'. There's a
dedicated macro in the kernel for exactly that usecase. Use that instead
to avoid possible errors and make the line shorter. The RTL930X code is
already doing it the good way.

Signed-off-by: Jonas Jelonek <jelonek.jonas@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/21410
Signed-off-by: Robert Marko <robimarko@gmail.com>