staging: speakup: avoid out-of-range access in synth_add()

commit 6102c48b upstream.

Check that array index is in-bounds before accessing the synths[] array.
Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Cc: Nickolai Zeldovich <nickolai@csail.mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/staging/speakup/synth.c

@@ -423,7 +423,7 @@ int synth_add(struct spk_synth *in_synth)
 	int i;
 	int status = 0;
 	mutex_lock(&spk_mutex);
-	for (i = 0; synths[i] != NULL && i < MAXSYNTHS; i++)
+	for (i = 0; i < MAXSYNTHS && synths[i] != NULL; i++)
 		/* synth_remove() is responsible for rotating the array down */
 		if (in_synth == synths[i]) {
 			mutex_unlock(&spk_mutex);