greybus: gpbridge: fix section mismatches

Fix section mismatches introduced by b27227ce93c0 ("greybus: Use
gb_gpbridge_protocol_init()"), which added __exit annotation to
gpbridge-protocol exit functions that are called in the error path of
gpbridge_init, which lives in the init section.

This triggered the following modpost warning:

	WARNING: modpost: Found 8 section mismatch(es).

Fixes: 16b33d100bff ("protocol: Add gb_gpbridge_protocol_driver()")
Fixes: b27227ce93c0 ("greybus: Use gb_gpbridge_protocol_init()")
Signed-off-by: Johan Hovold <johan@hovoldconsulting.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

drivers/staging/greybus/protocol.h

@@ -108,7 +108,7 @@ int __init gb_##__protocol##_init(void)			\
 {							\
 	return gb_protocol_register(&__protocol);	\
 }							\
-void __exit gb_##__protocol##_exit(void)		\
+void gb_##__protocol##_exit(void)			\
 {							\
 	gb_protocol_deregister(&__protocol);		\
 }							\