driver core: mark driver_allows_async_probing static

driver_allows_async_probing is only used in drivers/base/dd.c, so mark
it static and remove the declaration in drivers/base/base.h.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20221030092255.872280-1-hch@lst.deSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/base/base.h

@@ -146,7 +146,6 @@ static inline int driver_match_device(struct device_driver *drv,
 {
 	return drv->bus->match ? drv->bus->match(dev, drv) : 1;
 }
-extern bool driver_allows_async_probing(struct device_driver *drv);
 
 extern int driver_add_groups(struct device_driver *drv,
 			     const struct attribute_group **groups);

drivers/base/dd.c

@@ -843,7 +843,7 @@ static int __init save_async_options(char *buf)
 }
 __setup("driver_async_probe=", save_async_options);
 
-bool driver_allows_async_probing(struct device_driver *drv)
+static bool driver_allows_async_probing(struct device_driver *drv)
 {
 	switch (drv->probe_type) {
 	case PROBE_PREFER_ASYNCHRONOUS: