The alternative stub functions are listed as global, which produces
a build failure in some configs:

In file included from drivers/accel/qaic/qaic_drv.c:31:
drivers/accel/qaic/qaic_debugfs.h:16:5: error: no previous prototype for 'qaic_bootlog_register' [-Werror=missing-prototypes]
   16 | int qaic_bootlog_register(void) { return 0; }
      |     ^~~~~~~~~~~~~~~~~~~~~
drivers/accel/qaic/qaic_debugfs.h:17:6: error: no previous prototype for 'qaic_bootlog_unregister' [-Werror=missing-prototypes]
   17 | void qaic_bootlog_unregister(void) {}
      |      ^~~~~~~~~~~~~~~~~~~~~~~
drivers/accel/qaic/qaic_debugfs.h:18:6: error: no previous prototype for 'qaic_debugfs_init' [-Werror=missing-prototypes]
   18 | void qaic_debugfs_init(struct qaic_drm_device *qddev) {}
      |      ^~~~~~~~~~~~~~~~~

Make them static inline as intended.

Fixes: 5f8df5c6 ("accel/qaic: Add bootlog debugfs")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Jeffrey Hugo <quic_jhugo@quicinc.com>
Signed-off-by: Jeffrey Hugo <quic_jhugo@quicinc.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240409133945.2976190-1-arnd@kernel.org