shell: release flash device before probing

source/shell/flash.c

@@ -77,6 +77,11 @@ static void do_flash_probe(const char *s)
 {
 	(void)s;
 
+	if (flash) {
+		flash_release(flash);
+		flash = NULL;
+	}
+
 	flash = flash_probe();
 }