Merged the get_read_fd and get_write_fd requests.

diff --git a/server/mutex.c b/server/mutex.c
index 82b76c2..1adf373 100644
--- a/server/mutex.c
+++ b/server/mutex.c
@@ -39,8 +39,7 @@
     mutex_satisfied,           /* satisfied */
     NULL,                      /* get_poll_events */
     NULL,                      /* poll_event */
-    no_read_fd,                /* get_read_fd */
-    no_write_fd,               /* get_write_fd */
+    no_get_fd,                 /* get_fd */
     no_flush,                  /* flush */
     no_get_file_info,          /* get_file_info */
     mutex_destroy              /* destroy */