BUG/MINOR: ssl: fix memory leak at OCSP loading

Fix a memory leak when loading an OCSP file when the file was already
loaded elsewhere in the configuration.

Indeed, if the OCSP file already exists, a useless chunk_dup() will be
done during the load.

To fix it we reverts "ocsp" to "iocsp" like it was done previously.

This was introduced by commit 246c024 ("MINOR: ssl: load the ocsp
in/from the ckch").

Should fix part of the issue #746.

It must be backported in 2.1 and 2.2.
diff --git a/src/ssl_sock.c b/src/ssl_sock.c
index f98c5c0..9c094a5 100644
--- a/src/ssl_sock.c
+++ b/src/ssl_sock.c
@@ -1399,7 +1399,7 @@
 	ret = 0;
 
 	warn = NULL;
-	if (ssl_sock_load_ocsp_response(ckch->ocsp_response, ocsp, cid, &warn)) {
+	if (ssl_sock_load_ocsp_response(ckch->ocsp_response, iocsp, cid, &warn)) {
 		memprintf(&warn, "Loading: %s. Content will be ignored", warn ? warn : "failure");
 		ha_warning("%s.\n", warn);
 	}