tweak blockdev's help text

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
diff --git a/util-linux/blockdev.c b/util-linux/blockdev.c
index eb5914b..fea30b0 100644
--- a/util-linux/blockdev.c
+++ b/util-linux/blockdev.c
@@ -17,7 +17,7 @@
 //config:	  Performs some ioctls with block devices.
 
 //usage:#define blockdev_trivial_usage
-//usage:	"OPTION [OPTARG] DEVICE"
+//usage:	"OPTION BLOCKDEV"
 //usage:#define blockdev_full_usage "\n\n"
 //usage:       "Options:"
 //usage:     "\n	--setro		Set ro"