KVM: VMX: Reorder clearing of registers in the vCPU-run assembly flow

Move the clearing of the common registers (not 64-bit-only) to the start
of the flow that clears registers holding guest state.  This is
purely a cosmetic change so that the label doesn't point at a blank line
and a #define.

No functional change intended.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>