efivars: Use local variables instead of a pointer dereference

In order to support a compat interface we need to stop passing pointers
to structures around, since the type of structure is going to depend on
whether the current task is a compat task.

Cc: Mike Waychison <mikew@google.com>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>

diff --cc drivers/firmware/efi/efivars.c
Simple merge