efi: Add a sanity check to efivar_store_raw()

Add a sanity check to efivar_store_raw() the same way
efivar_{attr,size,data}_read() and efivar_show_raw() have it.

Signed-off-by: Vladis Dronov <vdronov@redhat.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20200305084041.24053-3-vdronov@redhat.com
Link: https://lore.kernel.org/r/20200308080859.21568-25-ardb@kernel.org