Fix FlexSPI2 speed setting, default to 88 MHz clock

teensy4/startup.c

 	IOMUXC_FLEXSPI2_IPP_IND_SCK_FA_SELECT_INPUT = 1; // GPIO_EMC_25 for Mode: ALT8
 
 	// turn on clock  (TODO: increase clock speed later, slow & cautious for first release)
-	CCM_CBCMR = (CCM_CBCMR & (CCM_CBCMR_FLEXSPI2_PODF_MASK | CCM_CBCMR_FLEXSPI2_CLK_SEL_MASK))
-		| CCM_CBCMR_FLEXSPI2_PODF(7) | CCM_CBCMR_FLEXSPI2_CLK_SEL(0); // 49.5 MHz
+	CCM_CBCMR = (CCM_CBCMR & ~(CCM_CBCMR_FLEXSPI2_PODF_MASK | CCM_CBCMR_FLEXSPI2_CLK_SEL_MASK))
+		| CCM_CBCMR_FLEXSPI2_PODF(5) | CCM_CBCMR_FLEXSPI2_CLK_SEL(3); // 88 MHz
 	CCM_CCGR7 |= CCM_CCGR7_FLEXSPI2(CCM_CCGR_ON);
 
 	FLEXSPI2_MCR0 |= FLEXSPI_MCR0_MDIS;