cmd/rng: fix long help text

The number of bytes may only be specified if a device number id provided.

Correct the formatting.

Acked-by: Marek BehĂșn <kabel@kernel.org>
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
diff --git a/cmd/rng.c b/cmd/rng.c
index 2fb7202..4d91094 100644
--- a/cmd/rng.c
+++ b/cmd/rng.c
@@ -75,6 +75,6 @@
 U_BOOT_CMD(
 	rng, 3, 0, do_rng,
 	"print bytes from the hardware random number generator",
-	"list         - list all the probed rng devices\n"
-	"rng [dev] [n]    - print n random bytes(max 64) read from dev\n"
+	"list          - list all probed rng devices\n"
+	"rng [dev [n]] - print n random bytes (max 64) read from dev\n"
 );