ubi: Fix fall-through warnings for Clang

In preparation to enable -Wimplicit-fallthrough for Clang, fix a warning
by explicitly adding a break statement instead of letting the code fall
through to the next case.

Link: https://github.com/KSPP/linux/issues/115
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Richard Weinberger <richard@nod.at>

drivers/mtd/ubi/build.c

@@ -1350,6 +1350,7 @@ static int bytes_str_to_int(const char *str)
 		fallthrough;
 	case 'K':
 		result *= 1024;
+		break;
 	case '\0':
 		break;
 	default: