modutils-initscripts: Bail out when no module is installed

Fix the following warning when boot with a core-image-minimal rootfs:
  depmod: can't change directory to 'lib/modules/5.10.25-yocto-standard': No such file or directory

Signed-off-by: Kevin Hao <kexin.hao@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>