staging: wilc1000: look for rtc_clk clock in spi mode

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: Adham Abozaeid <adham.abozaeid@microchip.com>
Link: https://lore.kernel.org/r/20190916193701.20755-1-adham.abozaeid@microchip.com


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