qemu: inline code for filling in per-VM NVRAM path

qemu: inline code for filling in per-VM NVRAM path

Before creating a NVRAM path, the qemuDomainNVRAMPathGenerate
method checks whether the config is using the old style
firmware approach. This check is redundant in one of the two
callers. By inlining the check into the other caller, it makes
it clearer to understand that the NVRAM path filling is done
conditionally.

Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>