realtek: RTL930x led_set count error message tidy up + dev_ print fixups

realtek: RTL930x led_set count error message tidy up + dev_ print fixups

Whilst testing Hasivo s1100wp-8gt-se LED configuration, several error
messages were presented which didn't indicate which led_set they were
referencing, nor what the value was that caused the invalid configuration.

Migrate to use dev_ print messages for this function.
And tidy up both when the error message is reported (don't show it when
an led_set isn't in the DTS) and what details the message presents.

Signed-off-by: Bevan Weiss <bevan.weiss@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/19791
Signed-off-by: Robert Marko <robimarko@gmail.com>