x86/kvm: Fix pr_info() for async PF setup/teardown

x86/kvm: Fix pr_info() for async PF setup/teardown

BugLink: https://bugs.launchpad.net/bugs/1920944
'pr_fmt' already has 'kvm-guest: ' so 'KVM' prefix is redundant.
"Unregister pv shared memory" is very ambiguous, it's hard to
say which particular PV feature it relates to.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20210414123544.1060604-2-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
(cherry picked from commit 0a269a008f837e76ce285679ab3005059fadc2a6)
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Acked-by: Guilherme G. Piccoli <gpiccoli@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>