MAINTAINERS: Add Jan Kara for filesystem DAX

Jan has been developing and reviewing filesystem DAX related changes for
quite a while now, and has agreed to help maintain this code going forward.

Thanks, Jan!

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Jan Kara <jack@suse.cz>
Signed-off-by: Dave Jiang <dave.jiang@intel.com>

MAINTAINERS

@@ -4270,6 +4270,7 @@ F:	drivers/i2c/busses/i2c-diolan-u2c.c
 FILESYSTEM DIRECT ACCESS (DAX)
 M:	Matthew Wilcox <mawilcox@microsoft.com>
 M:	Ross Zwisler <zwisler@kernel.org>
+M:	Jan Kara <jack@suse.cz>
 L:	linux-fsdevel@vger.kernel.org
 S:	Supported
 F:	fs/dax.c