[clang-tidy] Remove pointless const

The const is actually misplaced. const plist_t evaluates to void *const
instead of const void *. const qualification of the former makes no
sense in function declarations.

Found with misc-misplaced-const

Signed-off-by: Rosen Penev <rosenp@gmail.com>
diff --git a/src/plist.c b/src/plist.c
index 4d327e0..4cb6206 100644
--- a/src/plist.c
+++ b/src/plist.c
@@ -195,7 +195,7 @@
     return (plist_t) node_create(NULL, data);
 }
 
-plist_data_t plist_get_data(const plist_t node)
+plist_data_t plist_get_data(plist_t node)
 {
     if (!node)
         return NULL;
diff --git a/src/plist.h b/src/plist.h
index 7bf62a8..95d2a3e 100644
--- a/src/plist.h
+++ b/src/plist.h
@@ -65,7 +65,7 @@
 typedef struct plist_data_s *plist_data_t;
 
 plist_t plist_new_node(plist_data_t data);
-plist_data_t plist_get_data(const plist_t node);
+plist_data_t plist_get_data(plist_t node);
 plist_data_t plist_new_plist_data(void);
 void plist_free_data(plist_data_t data);
 int plist_data_compare(const void *a, const void *b);