spi_nxp_lpspi: Fix underflow in lpspi sck calculation

If `desired_delay_ns` is `0`, it is much saner to set the delay to `0x00`
than to underflow and set it to `0xff`, which is the current behavior.

Signed-off-by: Martin Stumpf <[email protected]>

Author: Finomnis

drivers/spi/spi_nxp_lpspi/spi_nxp_lpspi_common.c

@@ -132,7 +132,10 @@ static uint8_t lpspi_calc_delay_scaler(uint32_t desired_delay_ns,
 	delay_cycles = (uint64_t)prescaled_clock * desired_delay_ns;
 	delay_cycles = DIV_ROUND_UP(delay_cycles, NSEC_PER_SEC);
 
-       /* what the min_cycles parameter is about is that
+	/* clamp to minimally possible cycles to avoid underflow */
+	delay_cycles = MAX(delay_cycles, min_cycles);
+
+	/* what the min_cycles parameter is about is that
 	* PCSSCK and SCKPSC are +1 cycles of the programmed value,
 	* while DBT is +2 cycles of the programmed value.
 	* So this calculates the value to program to the register.