On DT systems the driver require a clock, but the probe just print a
warning and continue, leading to a crash when resetting the device.
To fix this crash and properly handle probe deferals only ignore the
missing clock if DT isn't used or if the clock doesn't exist.
Signed-off-by: Alban Bedel <alban.bedel@avionic-design.de> Acked-by: Iyappan Subramanian <isubramanian@apm.com> Signed-off-by: David S. Miller <davem@davemloft.net>