Fix the declaration of pthread_mutexattr_gettype().

diff --git a/loader/kthread.c b/loader/kthread.c
index cd74d54..6fae6be 100644
--- a/loader/kthread.c
+++ b/loader/kthread.c
@@ -654,7 +654,7 @@
 }
 strong_alias(__pthread_mutexattr_settype, pthread_mutexattr_settype);
 
-int __pthread_mutexattr_gettype(pthread_mutexattr_t *attr, int *kind)
+int __pthread_mutexattr_gettype(const pthread_mutexattr_t *attr, int *kind)
 {
   *kind = PTHREAD_MUTEX_RECURSIVE;
   return 0;