spi: pxa2xx: Constify struct driver_data parameter

In a couple of functions the contents of struct driver_data are not altered,
hence we may constify the respective function parameter.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20210510124134.24638-14-andriy.shevchenko@linux.intel.comSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-pxa2xx.h

@@ -93,7 +93,7 @@ static inline void pxa2xx_spi_write(const struct driver_data *drv_data, u32 reg,
 
 #define DMA_ALIGNMENT		8
 
-static inline int pxa25x_ssp_comp(struct driver_data *drv_data)
+static inline int pxa25x_ssp_comp(const struct driver_data *drv_data)
 {
 	switch (drv_data->ssp_type) {
 	case PXA25x_SSP:
@@ -115,7 +115,7 @@ static inline u32 read_SSSR_bits(const struct driver_data *drv_data, u32 bits)
 	return pxa2xx_spi_read(drv_data, SSSR) & bits;
 }
 
-static inline void write_SSSR_CS(struct driver_data *drv_data, u32 val)
+static inline void write_SSSR_CS(const struct driver_data *drv_data, u32 val)
 {
 	if (drv_data->ssp_type == CE4100_SSP ||
 	    drv_data->ssp_type == QUARK_X1000_SSP)