mtd: spi-nor: intel-spi: Simulate WRDI command

After spi_nor_write_disable() return code checks were introduced in the
spi-nor front end intel-spi backend stopped to work because WRDI was never
supported and always failed.

Just pretend it was sucessful and ignore the command itself. HW sequencer
shall do the right thing automatically, while with SW sequencer we cannot
do it anyway, because the only tool we had was preopcode and it makes no
sense for WRDI.

Fixes: bce679e5 ("mtd: spi-nor: Check for errors after each Register Operation")
Signed-off-by: Alexander Sverdlin <alexander.sverdlin@nokia.com>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/282e1305-fd08-e446-1a22-eb4dff78cfb4@nokia.comSigned-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>

drivers/mtd/spi-nor/controllers/intel-spi.c

@@ -612,6 +612,15 @@ static int intel_spi_write_reg(struct spi_nor *nor, u8 opcode, const u8 *buf,
 		return 0;
 	}
 
+	/*
+	 * We hope that HW sequencer will do the right thing automatically and
+	 * with the SW sequencer we cannot use preopcode anyway, so just ignore
+	 * the Write Disable operation and pretend it was completed
+	 * successfully.
+	 */
+	if (opcode == SPINOR_OP_WRDI)
+		return 0;
+
 	writel(0, ispi->base + FADDR);
 
 	/* Write the value beforehand */