sunxi_cedrus: Add string header to avoid build warning

Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>

src/sunxi_cedrus.c

@@ -42,6 +42,7 @@
 #include <stdlib.h>
 #include <stdio.h>
 
+#include <string.h>
 #include <unistd.h>
 #include <stdarg.h>
 #include <fcntl.h>