mtd: rawnand: Add a helper to clarify the interface configuration

Name it nand_interface_is_sdr() which will make even more sense when
nand_interface_is_nvddr() will be introduced.

Use it when relevant.
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20210505213750.257417-2-miquel.raynal@bootlin.com

drivers/mtd/nand/raw/atmel/nand-controller.c

@@ -1246,7 +1246,7 @@ static int atmel_smc_nand_prepare_smcconf(struct atmel_nand *nand,
 	nc = to_nand_controller(nand->base.controller);
 
 	/* DDR interface not supported. */
-	if (conf->type != NAND_SDR_IFACE)
+	if (!nand_interface_is_sdr(conf))
 		return -ENOTSUPP;
 
 	/*

include/linux/mtd/rawnand.h

@@ -496,6 +496,15 @@ struct nand_interface_config {
 	} timings;
 };
 
+/**
+ * nand_interface_is_sdr - get the interface type
+ * @conf:	The data interface
+ */
+static bool nand_interface_is_sdr(const struct nand_interface_config *conf)
+{
+	return conf->type == NAND_SDR_IFACE;
+}
+
 /**
  * nand_get_sdr_timings - get SDR timing from data interface
  * @conf:	The data interface
@@ -503,7 +512,7 @@ struct nand_interface_config {
 static inline const struct nand_sdr_timings *
 nand_get_sdr_timings(const struct nand_interface_config *conf)
 {
-	if (conf->type != NAND_SDR_IFACE)
+	if (!nand_interface_is_sdr(conf))
 		return ERR_PTR(-EINVAL);
 
 	return &conf->timings.sdr;