env: Move env_set() to env.h

Move env_set() over to the new header file.

Acked-by: Joe Hershberger <joe.hershberger@ni.com>
Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/cmd/ini.c b/cmd/ini.c
index 8c28fa6..f4faa7c 100644
--- a/cmd/ini.c
+++ b/cmd/ini.c
@@ -13,6 +13,7 @@
 
 #include <common.h>
 #include <command.h>
+#include <env.h>
 #include <environment.h>
 #include <linux/ctype.h>
 #include <linux/string.h>