Use the proper macro instead of hard coding fedora
    
    The efi-srpm-macros package contais a macro for the ESP vendor directory
    to make sure that the correct one for each distro is used. But the grub2
    package is instead hardcoding it to "fedora", use the macro instead.
    
    Signed-off-by: Benjamin Herrenschmidt <benh@amazon.com>
    Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>