efi: efivar_create_sysfs_entry() should return negative error codes

It's not very normal to return 1 on failure and 0 on success.  There
isn't a reason for it here, the callers don't care so long as it's
non-zero on failure.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>