libata: fix libata-core.c kernel-doc warning

Fix kernel-doc warning in libata-core.c:

Warning(..//drivers/ata/libata-core.c:4763): No description found for parameter 'tag'
Signed-off-by: NRandy Dunlap <rdunlap@infradead.org>
Signed-off-by: NTejun Heo <tj@kernel.org>

drivers/ata/libata-core.c

@@ -4754,6 +4754,7 @@ void swap_buf_le16(u16 *buf, unsigned int buf_words)
 /**
  *	ata_qc_new_init - Request an available ATA command, and initialize it
  *	@dev: Device from whom we request an available command structure
+ *	@tag: tag
  *
  *	LOCKING:
  *	None.