LU-812 replace get_sb with mount in struct file_system_type

LU-812 replace get_sb with mount in struct file_system_type

get_sb() has been removed from struct file_system_type since
2.6.39 and switched to mount().

Signed-off-by: James Simmons <uja.ornl@gmail.com>
Signed-off-by: Wally Wang <wang@cray.com>
Signed-off-by: Bob Glossman <bogl@whamcloud.com>
Change-Id: I6b0762828b26f065732f7f0c528e0b20d41cb710
Reviewed-on: http://review.whamcloud.com/3661
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>