firmware: rpi: Only create clocks device if we don't have a node for it

The firmware clocks driver was previously probed through a platform_device
created by the firmware driver.

Since we will now have a node for that clocks driver, we need to create the
device only in the case where there's no node for it already.

Reviewed-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Tested-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/72114c4287ebda2dbd952ea238d4489d359897e5.1592210452.git-series.maxime@cerno.tech


Signed-off-by: Stephen Boyd <sboyd@kernel.org>