Just like rtl8211f_led_hw_is_supported() and
rtl8211f_led_hw_control_set(), the rtl8211f_led_hw_control_get() also
needs to check the index value, otherwise the caller is likely to get
an incorrect rules.

Fixes: 17784801 ("net: phy: realtek: Add support for PHY LEDs on RTL8211F")
Signed-off-by: Hui Wang <hui.wang@canonical.com>
Reviewed-by: Marek Vasut <marex@denx.de>
Link: https://patch.msgid.link/20240927114610.1278935-1-hui.wang@canonical.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>