sound/oss/ac97_codec.c: restore MODULE_LICENSE

I accidentally removed the module license from sound/oss/ac97_codec.c in
commit 83bad1d764b836a482b88e0a1f44d7a5c3e1fee0 ("scheduled OSS driver
removal")

Spotted by Roland <devzero@web.de>.

Signed-off-by: Adrian Bunk <bunk@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/sound/oss/ac97_codec.c b/sound/oss/ac97_codec.c
index 87a6726..b63839e 100644
--- a/sound/oss/ac97_codec.c
+++ b/sound/oss/ac97_codec.c
@@ -1202,3 +1202,5 @@
 
 EXPORT_SYMBOL(ac97_probe_codec);
 
+MODULE_LICENSE("GPL");
+