The downstream QSDK kernel [1] and GCC_USB1_MOCK_UTMI_CLK are both 24MHz.
Adjust GCC_USB0_MOCK_UTMI_CLK to 24MHz to avoid the following error:

clk: couldn't set gcc_usb0_mock_utmi_clk clk rate to 20000000 (-22), current rate: 24000000

1. https://git.codelinaro.org/clo/qsdk/oss/kernel/linux-ipq-5.4/-/commit/486c8485f59

Fixes: 5726079c ("arm64: dts: ipq6018: Use reference clock to set dwc3 period")
Signed-off-by: Chukun Pan <amadeus@jmu.edu.cn>
Link: https://lore.kernel.org/r/20231218150805.1228160-1-amadeus@jmu.edu.cnSigned-off-by: Bjorn Andersson <andersson@kernel.org>