spi: cadence: Make cdns_mrvl_xspi_clk_div_list static

The sparse tool complains as follows:

drivers/spi/spi-cadence-xspi.c:334:11: warning:
	symbol 'cdns_mrvl_xspi_clk_div_list' was not declared. Should it be static?

This symbol is not used outside spi-cadence-xspi.c, so marks it static.
Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>
Link: https://patch.msgid.link/20240819120031.3884913-1-ruanjinjie@huawei.comSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-cadence-xspi.c

@@ -331,7 +331,7 @@ static struct cdns_xspi_driver_data cdns_driver_data = {
 	.mrvl_hw_overlay = false,
 };
 
-const int cdns_mrvl_xspi_clk_div_list[] = {
+static const int cdns_mrvl_xspi_clk_div_list[] = {
 	4,	//0x0 = Divide by 4.   SPI clock is 200 MHz.
 	6,	//0x1 = Divide by 6.   SPI clock is 133.33 MHz.
 	8,	//0x2 = Divide by 8.   SPI clock is 100 MHz.