staging: speakup: fix synth caching when synth init fails

synths[] array caches currently loaded synths. synth_add checks
synths[] before adding a new one. It however ignores the result of
do_synth_init. So when do_synth_init fails, the failed synth is still
cached. Since, as a result module loading fails too, synth_remove -
which is responsible for removing the cached synth - is never called.
Next time the failing synth is added again it succeeds because
synth_add finds it cached inside synths[].

This patch fixes this by caching a synth only after do_synth_init
succeeds.

Signed-off-by: Okash Khawaja <okash.khawaja@gmail.com>
Reviewed-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/speakup/synth.c

@@ -445,10 +445,15 @@ int synth_add(struct spk_synth *in_synth)
 		mutex_unlock(&spk_mutex);
 		return -1;
 	}
-	synths[i++] = in_synth;
-	synths[i] = NULL;
+
 	if (in_synth->startup)
 		status = do_synth_init(in_synth);
+
+	if (!status) {
+		synths[i++] = in_synth;
+		synths[i] = NULL;
+	}
+
 	mutex_unlock(&spk_mutex);
 	return status;
 }