staging: lustre: added a space between concatenated strings

A space has been inserted between two concatenated strings as required from
checkpatch.pl

These two updates do not lead to any problem as DFID is defined as a
string in ./drivers/staging/lustre/lustre/include/lustre/lustre_user.h

The script checkpatch.pl does not return any other warning/error.

Signed-off-by: Mario Bambagini <mario.bambagini@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>