There are valid cases where there is no way to translate a OF node to
a MMIO address via ranges, so do the same as the Linux kernel and don't
print an error message in that case, but make it available as a debug
message.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>