Update libhdfs engine documention and options

Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/options.c b/options.c
index 484efc1..3acfdc8 100644
--- a/options.c
+++ b/options.c
@@ -672,7 +672,7 @@
 		}
 		td->o.numa_memnodes = strdup(nodelist);
 		numa_free_nodemask(verify_bitmask);
-                
+
 		break;
 	case MPOL_LOCAL:
 	case MPOL_DEFAULT:
@@ -1542,7 +1542,7 @@
 			  },
 #endif
 #ifdef CONFIG_LIBHDFS
-			  { .ival = "hdfs",
+			  { .ival = "libhdfs",
 			    .help = "Hadoop Distributed Filesystem (HDFS) engine"
 			  },
 #endif