perf: Mark expected switch fall-through

In preparation to enabling -Wimplicit-fallthrough, mark switch cases
where we are expecting to fall through.

This patch fixes the following warning:

  kernel/events/core.c: In function ‘perf_event_parse_addr_filter’:
  kernel/events/core.c:9154:11: warning: this statement may fall through [-Wimplicit-fallthrough=]
      kernel = 1;
      ~~~~~~~^~~
  kernel/events/core.c:9156:3: note: here
     case IF_SRC_FILEADDR:
     ^~~~

Warning level 3 was used: -Wimplicit-fallthrough=3

This patch is part of the ongoing efforts to enable -Wimplicit-fallthrough.

Signed-off-by: Gustavo A. R. Silva <[email protected]>
Cc: Alexander Shishkin <[email protected]>
Cc: Gustavo A. R. Silva <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Kees Kook <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Link: http://lkml.kernel.org/r/20190212205430.GA8446@embeddedor
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>
diff --git a/kernel/events/core.c b/kernel/events/core.c
index dd9698a..6fb27b5 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -9175,6 +9175,7 @@ perf_event_parse_addr_filter(struct perf_event *event, char *fstr,
 		case IF_SRC_KERNELADDR:
 		case IF_SRC_KERNEL:
 			kernel = 1;
+			/* fall through */
 
 		case IF_SRC_FILEADDR:
 		case IF_SRC_FILE: