[PATCH] Revert "serdev: simplify Makefile"

[Johan Hovold]

This reverts commit 54edb425346a4d5e17f7e54e8c97c0d0eac26315.

The offending commit caused serdev core to always be built-in, something
which breaks the build of dependent modules when serdev is being built
as a module:

ERROR: "__serdev_device_driver_register" [drivers/gnss/gnss-ubx.ko] undefined!
...
make[2]: *** [/home/johan/work/omicron/src/linux/scripts/Makefile.modpost:94: __modpost] Error 1

Reported-by: kbuild test robot <lkp@xxxxxxxxx>
Signed-off-by: Johan Hovold <johan@xxxxxxxxxx>
---
 drivers/tty/serdev/Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/tty/serdev/Makefile b/drivers/tty/serdev/Makefile
index f71bb931735b..078417e5b068 100644
--- a/drivers/tty/serdev/Makefile
+++ b/drivers/tty/serdev/Makefile
@@ -1,6 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0
 serdev-objs := core.o
 
-obj-y += serdev.o
+obj-$(CONFIG_SERIAL_DEV_BUS) += serdev.o
 
 obj-$(CONFIG_SERIAL_DEV_CTRL_TTYPORT) += serdev-ttyport.o
-- 
2.24.1