doc: Fix typo in Doxyfile.core.in causing sources to be ignored

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
diff --git a/Doxyfile.core.in b/Doxyfile.core.in
index ee58f80..4baa3d5 100644
--- a/Doxyfile.core.in
+++ b/Doxyfile.core.in
@@ -610,7 +610,7 @@
 # directories like "/usr/src/myproject". Separate the files or directories
 # with spaces.
 
-INPUT                  = @srcdir@/include/osmocom/core @srcdir/@src
+INPUT                  = @srcdir@/include/osmocom/core @srcdir@/src
 
 # 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