buildroot

rtl8188eu: Move the post install target hook before the infras

The hook is only used to install firmware blobs, and so it
doesn't need to be declared after the kernel-module infra.
Move it where it belong, to avoid confusion.

Signed-off-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>