staging: lustre: llite: rw.c: remove gfp_mask

sparse reported that gfp_mask was of the wrong type to store gfp flags.  The
variable is not used so it can be removed.

Signed-off-by: Guillaume Morin <guillaume@morinfr.org>
Suggested-by:  <gregkh@linuxfoundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>