tools/env: allow equal sign as key value separation

Treat the first equal sign as a key/value separation too. This makes
the script files compatible with mkenvimage input file format. It
won't support variables with equal signs anymore, but this seems not
really like a loss.
Signed-off-by: NStefan Agner <stefan.agner@toradex.com>

tools/env/fw_env.c

@@ -357,7 +357,7 @@ static int get_config (char *);
 static char *skip_chars(char *s)
 {
 	for (; *s != '\0'; s++) {
-		if (isblank(*s))
+		if (isblank(*s) || *s == '=')
 			return s;
 	}
 	return NULL;