ifwitool: Fix calculation of dst_size

Change-Id: I07523252eacffb323e2bb54c306f5e9ac83e4cbd
Signed-off-by: Rolf Evers-Fischer <embedded24@evers-fischer.de>
Reviewed-on: https://review.coreboot.org/15162
Tested-by: build bot (Jenkins)
Reviewed-by: Furquan Shaikh <furquan@google.com>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>

util/cbfstool/ifwitool.c

@@ -1679,8 +1679,8 @@ static enum ifwi_ret ifwi_dir_replace(int type)
 	}
 
 	struct buffer dst;
-	size_t dst_size = buffer_size(&ifwi_image.subpart_buf[type] +
-				      buffer_size(&b) - s->e[i].length);
+	size_t dst_size = buffer_size(&ifwi_image.subpart_buf[type]) +
+				      buffer_size(&b) - s->e[i].length;
 	size_t subpart_start = s->e[i].offset;
 	size_t subpart_end = s->e[i].offset + s->e[i].length;