Need to explicitly include stdint.h for musl libc.

--- a/libffado/ffado.h.in	2016-10-03 18:42:35.335302853 +0200
+++ b/libffado/ffado.h.in	2016-10-03 18:43:56.999358778 +0200
@@ -31,6 +31,7 @@
 #define FFADO_MAX_NAME_LEN 256
 
 #include <stdlib.h>
+#include <stdint.h>
 
 #define FFADO_STREAMING_MAX_URL_LENGTH 2048