PCI: acpiphp: Allow built-in drivers for Attention Indicators

Since the introduction of the attention callback in acpiphp, a non-zero
struct module *owner has been required in acpiphp_register_attention(). The
intent seemed to be that the core code could hold a refcount on the module
while invoking a callback.

This check accidentally precludes the possibility of attention callbacks to
built-in drivers.

Remove the check on `struct module *owner` in acpiphp_register_attention()
so attention callbacks can also be registered from built-in drivers.

Link: https://lore.kernel.org/r/20230930002036.6491-1-scott@os.amperecomputing.com


Signed-off-by: D Scott Phillips <scott@os.amperecomputing.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>