conf: fix error message for wrong thread_pool_size
conf: fix error message for wrong thread_pool_size

Fix the copy-and-paste error by referring to the correct variable.

Fixes: 0df2e7df80452f81edbfeb0ee355235b533346a9
https://bugzilla.redhat.com/show_bug.cgi?id=2103132

Signed-off-by: Ján Tomko <4cab11cfb98d3c937327354a78eb07dbb6ee2bc6@redhat.com>

libvirt/libvirt,libvirt/libvirt,olafhering/libvirt,crobinso/libvirt,libvirt/libvirt,zippy2/libvirt,jfehlig/libvirt,olafhering/libvirt,crobinso/libvirt,zippy2/libvirt,zippy2/libvirt,libvirt/libvirt,crobinso/libvirt,jfehlig/libvirt,zippy2/libvirt,crobinso/libvirt,jfehlig/libvirt,olafhering/libvirt,jfehlig/libvirt,olafhering/libvirt