This can happen in cases like bug #102951[1], so add a proper debug msg
as done in wait_read. Also, change wait_read debug message to differ from
wait_write.

[1] https://bugzilla.kernel.org/show_bug.cgi?id=102951Signed-off-by: Marcos Paulo de Souza <marcos.souza.org@gmail.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>