bcma: fix build error when build as module

Currently of_default_bus_match_table is not exported so we can only use
this feature when bcma is build into the kernel. This patch removes
support for child buses when bcma is build as a module as a temporary
fix for a build problem introduces in this commit:

commit cae761b
Author: Rafał Miłecki <zajec5@gmail.com>
Date:   Sun Jun 28 17:17:13 2015 +0200

    bcma: populate bus DT subnodes as platform_device-s

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Fixes: cae761b ("bcma: populate bus DT subnodes as platform_device-s")
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

drivers/bcma/main.c

@@ -410,7 +410,11 @@ int bcma_bus_register(struct bcma_bus *bus)
 		bcma_core_pci_early_init(&bus->drv_pci[0]);
 	}
 
-	if (bus->host_pdev) {
+	/* TODO: remove check for IS_BUILTIN(CONFIG_BCMA) check when
+	 * of_default_bus_match_table is exported or in some other way
+	 * accessible. This is just a temporary workaround.
+	 */
+	if (IS_BUILTIN(CONFIG_BCMA) && bus->host_pdev) {
 		struct device *dev = &bus->host_pdev->dev;
 
 		of_platform_populate(dev->of_node, of_default_bus_match_table,