command.c: Enable auto tab for the editenv command

Enable the auto completion (with TAB) of the environment variable name
after the editenv command.

Signed-off-by: Ralf Trübenbach <ralf.truebenbach@men.de>
diff --git a/common/command.c b/common/command.c
index 0c66b7a..67ad692 100644
--- a/common/command.c
+++ b/common/command.c
@@ -188,6 +188,9 @@
 
 void install_auto_complete(void)
 {
+#if defined(CONFIG_CMD_EDITENV)
+	install_auto_complete_handler("editenv", var_complete);
+#endif
 	install_auto_complete_handler("printenv", var_complete);
 	install_auto_complete_handler("setenv", var_complete);
 #if defined(CONFIG_CMD_RUN)