cmd_usage: constify

The usage helper doesn't modify the command, so constify its input arg.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>

common/command.c

diff --git a/common/command.c b/common/command.c
index b3ec510..ddaed68 100644
--- a/common/command.c
+++ b/common/command.c
@@ -140,7 +140,7 @@
 	return find_cmd_tbl(cmd, &__u_boot_cmd_start, len);
 }
 
-int cmd_usage(cmd_tbl_t *cmdtp)
+int cmd_usage(const cmd_tbl_t *cmdtp)
 {
 	printf("%s - %s\n\n", cmdtp->name, cmdtp->usage);
 

include/command.h

diff --git a/include/command.h b/include/command.h
index 37e118c..f1accd0 100644
--- a/include/command.h
+++ b/include/command.h
@@ -71,7 +71,7 @@
 cmd_tbl_t *find_cmd(const char *cmd);
 cmd_tbl_t *find_cmd_tbl (const char *cmd, cmd_tbl_t *table, int table_len);
 
-extern int cmd_usage(cmd_tbl_t *cmdtp);
+extern int cmd_usage(const cmd_tbl_t *cmdtp);
 
 #ifdef CONFIG_AUTO_COMPLETE
 extern int var_complete(int argc, char * const argv[], char last_char, int maxv, char *cmdv[]);