staging: wilc1000: look for rtc_clk clock

If rtc_clk is provided from DT, use it and enable it.
This is optional.
The signal may be hardcoded and no need to be requested,
but if DT provides it, use it.

Signed-off-by: Eugen Hristev <eugen.hristev@microchip.com>
Acked-by: Ajay Singh <ajay.kathat@microchip.com>
Link: https://lore.kernel.org/r/1568037993-4646-2-git-send-email-eugen.hristev@microchip.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>