KVM: arm64: Remove redundant Spectre-v2 code from kvm_map_vector()

'__kvm_bp_vect_base' is only used when dealing with the hardened vectors
so remove the redundant assignments in kvm_map_vectors().

Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Quentin Perret <qperret@google.com>
Link: https://lore.kernel.org/r/20201113113847.21619-2-will@kernel.org