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>

include/linux/isa.h

@@ -6,6 +6,7 @@
 #define __LINUX_ISA_H
 
 #include <linux/device.h>
+#include <linux/errno.h>
 #include <linux/kernel.h>
 
 struct isa_driver {
@@ -28,7 +29,7 @@ void isa_unregister_driver(struct isa_driver *);
 #else
 static inline int isa_register_driver(struct isa_driver *d, unsigned int i)
 {
-	return 0;
+	return -ENODEV;
 }
 
 static inline void isa_unregister_driver(struct isa_driver *d)