target: merge release_cmd methods

The release_cmd_to_pool and release_cmd_direct methods are always the same.
Merge them into a single release_cmd method, and clean up the fallout.

(nab: fix breakage in transport_generic_free_cmd() parameter build breakage
 in drivers/target/tcm_fc/tfc_cmd.c)

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
diff --git a/drivers/target/target_core_configfs.c b/drivers/target/target_core_configfs.c
index aac0ee9..63cba1e 100644
--- a/drivers/target/target_core_configfs.c
+++ b/drivers/target/target_core_configfs.c
@@ -427,12 +427,8 @@
 		printk(KERN_ERR "Missing tfo->tpg_get_inst_index()\n");
 		return -EINVAL;
 	}
-	if (!(tfo->release_cmd_to_pool)) {
-		printk(KERN_ERR "Missing tfo->release_cmd_to_pool()\n");
-		return -EINVAL;
-	}
-	if (!(tfo->release_cmd_direct)) {
-		printk(KERN_ERR "Missing tfo->release_cmd_direct()\n");
+	if (!tfo->release_cmd) {
+		printk(KERN_ERR "Missing tfo->release_cmd()\n");
 		return -EINVAL;
 	}
 	if (!(tfo->shutdown_session)) {