docs: virt/kvm: close inline string literal

This fixes

	Documentation/virt/kvm/amd-memory-encryption.rst:76: WARNING: Inline literal start-string without end-string.

Fixes: 2da1ed62 ("KVM: SVM: document KVM_MEM_ENCRYPT_OP, let userspace detect if SEV is available")
Signed-off-by: Stephen Kitt <steve@sk2.org>
Link: https://lore.kernel.org/r/20200424152637.120876-1-steve@sk2.org


Signed-off-by: Jonathan Corbet <corbet@lwn.net>