Hello tyassin1,
The register of "SPI0CLKSEL" is included in FCLKSEL[11];
You can configuration the SPI clock through as below code in SDK:
/* Attach main clock to SPI0. */
CLOCK_Select(kSPI0_Clk_From_MainClk);
BTW, recommend you refer to the SPI demo under SDK for lpc845MAX board.
BR
Alice