Add the const qualifier to "char *" variables that refer to literal strings. (#4370)

diff --git a/Modules/ossaudiodev.c b/Modules/ossaudiodev.c
index 8bb4d0d..58ee71f 100644
--- a/Modules/ossaudiodev.c
+++ b/Modules/ossaudiodev.c
@@ -53,7 +53,7 @@
 
 typedef struct {
     PyObject_HEAD
-    char    *devicename;              /* name of the device file */
+    const char *devicename;           /* name of the device file */
     int      fd;                      /* file descriptor */
     int      mode;                    /* file mode (O_RDONLY, etc.) */
     Py_ssize_t icount;                /* input count */
@@ -82,8 +82,8 @@
 {
     oss_audio_t *self;
     int fd, afmts, imode;
-    char *devicename = NULL;
-    char *mode = NULL;
+    const char *devicename = NULL;
+    const char *mode = NULL;
 
     /* Two ways to call open():
          open(device, mode) (for consistency with builtin open())
@@ -167,7 +167,7 @@
 static oss_mixer_t *
 newossmixerobject(PyObject *arg)
 {
-    char *devicename = NULL;
+    const char *devicename = NULL;
     int fd;
     oss_mixer_t *self;