net: dsa: ks8995: Add proper RESET delay

According to the datasheet we need to wait 100us before accessing
any registers in the KS8995 after a reset de-assertion.

Add this delay, if and only if we obtained a GPIO descriptor,
otherwise it is just a pointless delay.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/20250813-ks8995-to-dsa-v1-2-75c359ede3a5@linaro.org


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