mtd: spi-nor: missing fallthrough in set_4byte()

Add a missing fallthrough macro to avoid a -Wimplicit-fallthrough warning.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Jagan Teki <jagan@amarulasolutions.com>
diff --git a/drivers/mtd/spi/spi-nor-core.c b/drivers/mtd/spi/spi-nor-core.c
index 83d7fe4..f963ed0 100644
--- a/drivers/mtd/spi/spi-nor-core.c
+++ b/drivers/mtd/spi/spi-nor-core.c
@@ -669,6 +669,7 @@
 	case SNOR_MFR_MICRON:
 		/* Some Micron need WREN command; all will accept it */
 		need_wren = true;
+		fallthrough;
 	case SNOR_MFR_ISSI:
 	case SNOR_MFR_MACRONIX:
 	case SNOR_MFR_WINBOND: