arm64: dts: ipq6018: Use reference clock to set dwc3 period

arm64: dts: ipq6018: Use reference clock to set dwc3 period

Instead of manually setting snps,ref-clock-period-ns, we can let the
driver calculate it automatically from the "ref" clock. I haven't
reviewed this board's schematics, so please let me know if this is the
wrong 24MHz clock to use.

Signed-off-by: Sean Anderson <sean.anderson@seco.com>
Link: https://lore.kernel.org/r/20220127200636.1456175-8-sean.anderson@seco.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>