MAINTAINERS: add missed trace file for f2fs

This patch adds missed trace file in maintainer-ship of f2fs,
so it completes the description of files maintained in f2fs,
and also it allows people to find correct mailing list by using
get_maintainer.pl when only patching the trace file of f2fs.
Signed-off-by: NChao Yu <chao2.yu@samsung.com>
Signed-off-by: NJaegeuk Kim <jaegeuk@kernel.org>

MAINTAINERS

@@ -4414,6 +4414,7 @@ F:	Documentation/filesystems/f2fs.txt
 F:	Documentation/ABI/testing/sysfs-fs-f2fs
 F:	fs/f2fs/
 F:	include/linux/f2fs_fs.h
+F:	include/trace/events/f2fs.h
 
 FUJITSU FR-V (FRV) PORT
 M:	David Howells <dhowells@redhat.com>