Fix a warning on some compilers.

tests/test_common/ma_test_common.c

@@ -25,7 +25,7 @@ typedef struct
     ma_test_entry_proc onEntry;
 } ma_test;
 
-struct
+static struct
 {
     ma_test pTests[MAX_TESTS];
     size_t count;

tests/test_deviceio/ma_test_deviceio.c

@@ -51,7 +51,7 @@ typedef enum
     source_type_decoder
 } source_type;
 
-struct
+static struct
 {
     ma_context context;
     ma_device device;