The watchdog driver of the SoC uses the clk API to
get the clock associated with the watchdog device.
However the MT7620 specific setup code does not
register a clock for the watchdog device yet which
leads to the following error:

  rt2880_wdt: probe of 10000120.watchdog failed with error -2

Register a clock device for the watchdog in order to
avoid the error and make the watchdog usable.
Signed-off-by: NJohn Crispin <blogic@openwrt.org>
Signed-off-by: NGabor Juhos <juhosg@openwrt.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/5756/Signed-off-by: NRalf Baechle <ralf@linux-mips.org>