kvm: nVMX: match comment with return type for nested_vmx_exit_reflected

nested_vmx_exit_reflected() returns a bool, not int. As such, refer to
the return values as true/false in the comment instead of 1/0.

Signed-off-by: Oliver Upton <oupton@google.com>
Message-Id: <20200414221241.134103-1-oupton@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>