efi: Small leak on error in runtime map code

The "> 0" here should ">= 0" so we free map_entries[0].

Fixes: 926172d4 ('efi: Export EFI runtime memory mapping to sysfs')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Dave Young <dyoung@redhat.com>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>