can: tcan4x5x: remove regmap async support

The driver doesn't use regmap async support, so remove the stubs.
Reviewed-by: Dan Murphy <dmurphy@ti.com>
Tested-by: Sean Nyekjaer <sean@geanix.com>
Link: https://lore.kernel.org/r/20201215231746.1132907-8-mkl@pengutronix.deSigned-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/m_can/tcan4x5x-regmap.c

@@ -44,19 +44,6 @@ static int tcan4x5x_regmap_write(void *context, const void *data, size_t count)
 	return regmap_spi_gather_write(context, reg, 4, val, count - 4);
 }
 
-static int regmap_spi_async_write(void *context,
-				  const void *reg, size_t reg_len,
-				  const void *val, size_t val_len,
-				  struct regmap_async *a)
-{
-	return -ENOTSUPP;
-}
-
-static struct regmap_async *regmap_spi_async_alloc(void)
-{
-	return NULL;
-}
-
 static int tcan4x5x_regmap_read(void *context,
 				const void *reg, size_t reg_size,
 				void *val, size_t val_size)
@@ -79,8 +66,6 @@ static const struct regmap_config tcan4x5x_regmap = {
 static const struct regmap_bus tcan4x5x_bus = {
 	.write = tcan4x5x_regmap_write,
 	.gather_write = regmap_spi_gather_write,
-	.async_write = regmap_spi_async_write,
-	.async_alloc = regmap_spi_async_alloc,
 	.read = tcan4x5x_regmap_read,
 	.reg_format_endian_default = REGMAP_ENDIAN_NATIVE,
 	.val_format_endian_default = REGMAP_ENDIAN_NATIVE,