boot cmds: convert to getenv_yesno() with autostart

Use the new helper func to clean up duplicate logic handling of the
autostart env var.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
diff --git a/common/cmd_ide.c b/common/cmd_ide.c
index df7bdf5..f6278812 100644
--- a/common/cmd_ide.c
+++ b/common/cmd_ide.c
@@ -496,7 +496,7 @@
 	load_addr = addr;
 
 	/* Check if we should attempt an auto-start */
-	if (((ep = getenv("autostart")) != NULL) && (strcmp(ep,"yes") == 0)) {
+	if (getenv_yesno("autostart")) {
 		char *local_args[2];
 
 		local_args[0] = argv[0];