staging: intel_sst: fix signess error

str_id was unsigned, so check for (str_id <= 0) made no sense.
Made it signed.

Signed-off-by: Vasiliy Kulikov <segooon@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/staging/intel_sst/intel_sst_stream.c

@@ -117,7 +117,8 @@ int sst_alloc_stream(char *params, unsigned int stream_ops,
 {
 	struct ipc_post *msg = NULL;
 	struct snd_sst_alloc_params alloc_param;
-	unsigned int pcm_slot = 0, num_ch, str_id;
+	unsigned int pcm_slot = 0, num_ch;
+	int str_id;
 	struct snd_sst_stream_params *sparams;
 	struct stream_info *str_info;