mtd: spi-nand: Expose spinand_write_reg_op()

This helper function will soon be used from a vendor driver, let's
export it through the spinand.h header. No need for any export, as there
is currently no reason for any module to need it.
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20240826101412.20644-6-miquel.raynal@bootlin.com

drivers/mtd/nand/spi/core.c

@@ -34,7 +34,7 @@ static int spinand_read_reg_op(struct spinand_device *spinand, u8 reg, u8 *val)
 	return 0;
 }
 
-static int spinand_write_reg_op(struct spinand_device *spinand, u8 reg, u8 val)
+int spinand_write_reg_op(struct spinand_device *spinand, u8 reg, u8 val)
 {
 	struct spi_mem_op op = SPINAND_SET_FEATURE_OP(reg,
 						      spinand->scratchbuf);

include/linux/mtd/spinand.h

@@ -533,6 +533,7 @@ int spinand_match_and_init(struct spinand_device *spinand,
 			   enum spinand_readid_method rdid_method);
 
 int spinand_upd_cfg(struct spinand_device *spinand, u8 mask, u8 val);
+int spinand_write_reg_op(struct spinand_device *spinand, u8 reg, u8 val);
 int spinand_select_target(struct spinand_device *spinand, unsigned int target);
 
 #endif /* __LINUX_MTD_SPINAND_H */