env: Move env_get() to env.h

Move env_get() 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/common/cli.c b/common/cli.c
index f4054fb..49b9106 100644
--- a/common/cli.c
+++ b/common/cli.c
@@ -12,6 +12,7 @@
 #include <cli.h>
 #include <cli_hush.h>
 #include <console.h>
+#include <env.h>
 #include <fdtdec.h>
 #include <malloc.h>