cifs: remove unused value pointed out by Coverity

Detected by CoverityScan CID#1438719 ("Unused Value")

buf is reset again before being used so these two lines of code
are useless.
Signed-off-by: NSteve French <stfrench@microsoft.com>
Reviewed-by: NRonnie Sahlberg <lsahlber@redhat.com>

fs/cifs/connect.c

@@ -1191,10 +1191,6 @@ cifs_demultiplex_thread(void *p)
 			continue;
 		}
 
-		if (server->large_buf)
-			buf = server->bigbuf;
-
-
 		server->lstrp = jiffies;
 
 		for (i = 0; i < num_mids; i++) {