staging: lustre: remove ALLOC_ATOMIC_TRY

Come on, is it so hard to type "GFP_ATOMIC"?  Look, it's less
characters!!!

Cc: Andreas Dilger <andreas.dilger@intel.com>
Cc: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>