staging: lustre: lustre: mdc: lproc_mdc.c: Fix for potential NULL pointer dereference

In mdc_kuc_write(), OBD_ALLOC(lh, len) may leave 'lh' to NULL as kmalloc
may fail to allocate memory. This fix adds a check to avoid, dereferencing
a NULL pointer.

Signed-off-by: Kumar Amit Mehta <gmate.amit@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>