driver core: fix build with SYSFS=n

When SYSFS=n and MODULES=y, build ends with:

linux-2.6.24-rc6-mm1/drivers/base/module.c: In function 'module_add_driver':
linux-2.6.24-rc6-mm1/drivers/base/module.c:49: error: 'module_kset' undeclared (first use in this function)
make[3]: *** [drivers/base/module.o] Error 1

Below is one possible fix.
Build-tested with all 4 config combinations of SYSFS & MODULES.

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/drivers/base/base.h b/drivers/base/base.h
index a74ceda..f7ad65a 100644
--- a/drivers/base/base.h
+++ b/drivers/base/base.h
@@ -81,7 +81,7 @@
 
 extern struct kset *devices_kset;
 
-#ifdef CONFIG_MODULES
+#if defined(CONFIG_MODULES) && defined(CONFIG_SYSFS)
 extern void module_add_driver(struct module *mod, struct device_driver *drv);
 extern void module_remove_driver(struct device_driver *drv);
 #else