seq: Fix wrong FB direction at snd_seq_create_ump_block()

snd_seq_create_ump_block() receives a snd_ump_block_info_t data at the
creation of a FB and updates its associated sequencer port, but it
handled the port direction incorrectly.  The UMP / port direction
means the connectivity, but the current code translated other way
round.  The correct translation should be that input = receiver, i.e.
a writable port for applications, and output = source, a readable port
for applications.

This patch corrects the translation, and add more comments to the
direction definition.

Signed-off-by: Takashi Iwai <tiwai@suse.de>

include/seq.h

@@ -250,8 +250,8 @@ typedef struct _snd_seq_port_info snd_seq_port_info_t;
 
 /** port direction */
 #define SND_SEQ_PORT_DIR_UNKNOWN	0	/**< Unknown */
-#define SND_SEQ_PORT_DIR_INPUT		1	/**< Input only */
-#define SND_SEQ_PORT_DIR_OUTPUT		2	/**< Output only */
+#define SND_SEQ_PORT_DIR_INPUT		1	/**< Input only; sink, receiver */
+#define SND_SEQ_PORT_DIR_OUTPUT		2	/**< Output only; source, transmitter */
 #define SND_SEQ_PORT_DIR_BIDIRECTION	3	/**< Input/output bidirectional */
 
 /* port type */

src/seq/seqmid.c

@@ -645,16 +645,16 @@ static void update_group_ports(snd_seq_t *seq, snd_ump_endpoint_info_t *ep)
 			    i >= bp->first_group + bp->num_groups)
 				continue;
 			switch (bp->direction) {
-			case SNDRV_UMP_DIR_INPUT:
-				caps |= SNDRV_SEQ_PORT_CAP_READ |
-					SNDRV_SEQ_PORT_CAP_SYNC_READ |
-					SNDRV_SEQ_PORT_CAP_SUBS_READ;
-				break;
-			case SNDRV_UMP_DIR_OUTPUT:
+			case SNDRV_UMP_DIR_INPUT: /* sink, receiver */
 				caps |= SNDRV_SEQ_PORT_CAP_WRITE |
 					SNDRV_SEQ_PORT_CAP_SYNC_WRITE |
 					SNDRV_SEQ_PORT_CAP_SUBS_WRITE;
 				break;
+			case SNDRV_UMP_DIR_OUTPUT: /* source, transmitter */
+				caps |= SNDRV_SEQ_PORT_CAP_READ |
+					SNDRV_SEQ_PORT_CAP_SYNC_READ |
+					SNDRV_SEQ_PORT_CAP_SUBS_READ;
+				break;
 			case SNDRV_UMP_DIR_BIDIRECTION:
 				caps |= SNDRV_SEQ_PORT_CAP_READ |
 					SNDRV_SEQ_PORT_CAP_SYNC_READ |