LU-4423 lov: check return value of lov_sub_get()

LU-4423 lov: check return value of lov_sub_get()

Check return value of lov_sub_get() in lov_io_read_ahead().

Linux-commit: f99e73a5e3ff556bc69e5e592fee18d4cb7600dd

Signed-off-by: Jinshan Xiong <jinshan.xiong@intel.com>
Change-Id: Ic5403664c649b8f41861cf1bbfc68ab9ef537a15
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-on: https://review.whamcloud.com/23618
Tested-by: Jenkins
Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>