selftests: KVM: Fix check for !POLLIN in demand_paging_test

The logical not operator applies only to the left hand side of a bitwise
operator. As such, the check for POLLIN not being set in revents wrong.
Fix it by adding parentheses around the bitwise expression.

Fixes: 4f72180eb4 ("KVM: selftests: Add demand paging content to the demand paging test")
Reviewed-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Oliver Upton <oupton@google.com>
Message-Id: <20210921171121.2148982-2-oupton@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

tools/testing/selftests/kvm/demand_paging_test.c

@@ -179,7 +179,7 @@ static void *uffd_handler_thread_fn(void *arg)
 			return NULL;
 		}
 
-		if (!pollfd[0].revents & POLLIN)
+		if (!(pollfd[0].revents & POLLIN))
 			continue;
 
 		r = read(uffd, &msg, sizeof(msg));