module: make module_refcount() a signed integer.

James Bottomley points out that it will be -1 during unload.  It's
only used for diagnostics, so let's not hide that as it could be a
clue as to what's gone wrong.

Cc: Jason Wessel <jason.wessel@windriver.com>
Acked-and-documention-added-by: James Bottomley <James.Bottomley@HansenPartnership.com>
Reviewed-by: Masami Hiramatsu <maasami.hiramatsu.pt@hitachi.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
diff --git a/include/linux/module.h b/include/linux/module.h
index ebfb0e1..b653d7c 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -444,7 +444,7 @@
 #define module_put_and_exit(code) __module_put_and_exit(THIS_MODULE, code)
 
 #ifdef CONFIG_MODULE_UNLOAD
-unsigned long module_refcount(struct module *mod);
+int module_refcount(struct module *mod);
 void __symbol_put(const char *symbol);
 #define symbol_put(x) __symbol_put(VMLINUX_SYMBOL_STR(x))
 void symbol_put_addr(void *addr);