ASoC: fsl_sai: mark regmap as fast_io

The regmap is only ever used to access MMIO registers, so it's fair
to say that register access is fast.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Link: https://lore.kernel.org/r/20190717105156.15721-1-l.stach@pengutronix.de
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/fsl/fsl_sai.c

@@ -763,6 +763,7 @@ static const struct regmap_config fsl_sai_regmap_config = {
 	.reg_bits = 32,
 	.reg_stride = 4,
 	.val_bits = 32,
+	.fast_io = true,
 
 	.max_register = FSL_SAI_RMR,
 	.reg_defaults = fsl_sai_reg_defaults,