staging: lustre: lustre: mdc: mdc_lib.c: Removed an unnecessary NULL check

Removed an unnecessary NULL check.
I have checked the only place this function is called from.

Signed-off-by: Rickard Strandqvist <rickard_strandqvist@spectrumdigital.se>
Reviewed-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>