KVM: selftests: Slightly simplify memstress_setup_nested()

KVM: selftests: Slightly simplify memstress_setup_nested()

Instead of calling memstress_setup_ept_mappings() only in the first
iteration in the loop, move it before the loop.

The call needed to happen within the loop before commit e40e72fec0de
("KVM: selftests: Stop passing VMX metadata to TDP mapping functions"),
as memstress_setup_ept_mappings() used to take in a pointer to vmx_pages
and pass it into tdp_identity_map_1g() (to get the EPT root GPA). This
is no longer the case, as tdp_identity_map_1g() gets the EPT root
through stage2 MMU.

Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>
Link: https://patch.msgid.link/20260113171456.2097312-1-yosry.ahmed@linux.dev
Signed-off-by: Sean Christopherson <seanjc@google.com>