isa: Dummy isa_register_driver should return error code

The inline isa_register_driver stub simply allows compilation on systems
with CONFIG_ISA disabled; the dummy isa_register_driver does not
register an isa_driver at all. The inline isa_register_driver should
return -ENODEV to indicate lack of support when attempting to register
an isa_driver on such a system with CONFIG_ISA disabled.

Cc: Matthew Wilcox <matthew@wil.cx>
Reported-by: Sasha Levin <sasha.levin@oracle.com>
Tested-by: Ye Xiaolong
Signed-off-by: William Breathitt Gray <vilhelm.gray@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>