Staging: lustre: mdc_locks: Remove extra test expression

struct it is already NULL tested before so, it should be removed from
the if test expression.

Signed-off-by: Shivani Bhardwaj <shivanib134@gmail.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>