video/fbdev/stifb: Fix spelling mistake in fall-through annotation

Replace "fall though" with a proper "fall through" annotation.

This fix is part of the ongoing efforts to enabling
-Wimplicit-fallthrough

Addresses-Coverity-ID: 402013 ("Missing break in switch")
Signed-off-by: Gustavo A. R. Silva <[e-mail]>
Cc: "James E.J. Bottomley" <[e-mail]>
Cc: Helge Deller <[e-mail]>
Signed-off-by: Bartlomiej Zolnierkiewicz <[e-mail]>

drivers/video/fbdev/stifb.c

···
 			dev_name);
 		   goto out_err0;
 		}
-		/* fall though */
+		/* fall through */
 	case S9000_ID_ARTIST:
 	case S9000_ID_HCRX:
 	case S9000_ID_TIMBER: