doxygen: make sure the right C source files are included
diff --git a/Doxyfile.gsm b/Doxyfile.gsm
index ac2b28b..9fabac7 100644
--- a/Doxyfile.gsm
+++ b/Doxyfile.gsm
@@ -610,7 +610,7 @@
 # directories like "/usr/src/myproject". Separate the files or directories
 # with spaces.
 
-INPUT                  = include/osmocom/gsm src/gsm/*.c
+INPUT                  = include/osmocom/gsm src/gsm
 
 # This tag can be used to specify the character encoding of the source files
 # that doxygen parses. Internally doxygen uses the UTF-8 encoding, which is