test: missing header

Signed-off-by: Slawomir Blauciak <slawomir.blauciak@linux.intel.com>

Author: slawblauciak

test/cmocka/src/audio/buffer/mock.c

@@ -31,6 +31,8 @@
 #include <stdint.h>
 #include <stdlib.h>
 
+#include <sof/alloc.h>
+
 void _trace_event(uint32_t e)
 {
 	(void)e;