cmd_part: fix typo in part command help text

All the sub-commands start with the main command name, but it was
missing from one of the help texts.

<panto> typos fix.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Tom Rini <trini@ti.com>
Acked-by: Pantelis Antoniou <panto@antoniou-consulting.com>

common/cmd_part.c

@@ -82,7 +82,7 @@ int do_part(cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
 U_BOOT_CMD(
 	part,	5,	1,	do_part,
 	"disk partition related commands",
-	"uuid <interface> <dev>:<part>\n"
+	"part uuid <interface> <dev>:<part>\n"
 	"    - print partition UUID\n"
 	"part uuid <interface> <dev>:<part> <varname>\n"
 	"    - set environment variable to partition UUID\n"