staging: lustre: fix 'NULL pointer dereference' errors

Fix 'NULL pointer dereference' defects found by Coverity version
6.5.0:
Dereference after null check (FORWARD_NULL)
For instance, Passing null pointer to a function which dereferences
it.
Dereference before null check (REVERSE_INULL)
Null-checking variable suggests that it may be null, but it has
already been dereferenced on all paths leading to the check.
Dereference null return value (NULL_RETURNS)

Signed-off-by: Sebastien Buisson <sbuisson@ddn.com>
Signed-off-by: James Nunez <james.a.nunez@intel.com>
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-3042
Reviewed-on: http://review.whamcloud.com/5868


Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: James Simmons <jsimmons@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>