driver core: export subsys_virtual_register

Modules want to call this function, so it needs to be exported.

Reported-by: Daniel Mack <zonque@gmail.com>
Cc: Kay Sievers <kay@vrfy.org>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/base/bus.c b/drivers/base/bus.c
index 1a68f947..d414331 100644
--- a/drivers/base/bus.c
+++ b/drivers/base/bus.c
@@ -1295,6 +1295,7 @@
 
 	return subsys_register(subsys, groups, virtual_dir);
 }
+EXPORT_SYMBOL_GPL(subsys_virtual_register);
 
 int __init buses_init(void)
 {