SPI: Fix discarded-qalifiers warning when compiling with all warnings (espressif#3458)

* SPI: Fix discarded-qalifiers warning when compiling with all warnings This fixes an error introduced with changeset b847f41 which tightened the use of const for read-only data. The helper funtion __transferBytes also requires the const qualifier on outgoing data. Without this change a warning is displayed when compiling with the Arduino IDE set to display "All" compiler warnings. Tests: - Build an ESP32 SPI sketch that uses static const data to send to an SPI device using the SPI.transferBytes() API * SPI:Ensure all local functions are marked static This audits all functions in the esp32-hal-xpi.c module and ensures that any functions entirely local to the module are marked as static. Tests: - Build with Arduino set to show all warnings and ensure none are displayed * SPI: Remove unused local __spiTranslate24 function This removes the __spiTranslate24() function which is unused.

Author: davefiddes

cores/esp32/esp32-hal-spi.c

@@ -532,17 +532,7 @@ uint8_t spiTransferByte(spi_t * spi, uint8_t data)
  return data;
 }
 
-uint32_t __spiTranslate24(uint32_t data)
-{
- union {
- uint32_t l;
- uint8_t b[4];
- } out;
- out.l = data;
- return out.b[2] | (out.b[1] << 8) | (out.b[0] << 16);
-}
-
-uint32_t __spiTranslate32(uint32_t data)
+static uint32_t __spiTranslate32(uint32_t data)
 {
  union {
  uint32_t l;
@@ -630,7 +620,7 @@ uint32_t spiTransferLong(spi_t * spi, uint32_t data)
  return data;
 }
 
-void __spiTransferBytes(spi_t * spi, uint8_t * data, uint8_t * out, uint32_t bytes)
+static void __spiTransferBytes(spi_t * spi, const uint8_t * data, uint8_t * out, uint32_t bytes)
 {
  if(!spi) {
  return;