ANDROID: serdev: Fix platform device support

After commit cdad3113 ("ANDROID: serdev: add platform device
support") landed, we started seeing boot panics on HiKey960/HiKey.

After some debugging I found the patch is passing a serdev_device->dev
pointer to match()/uevent(), which expects the dev pointer to be
contained in a platform_device structure instead. When it uses
container_of, it ends up miscast and we get bad values.

Alistair suggested this fix which seems to avoid the issue.

Signed-off-by: John Stultz <john.stultz@linaro.org>
Bug: 146517987
Change-Id: I6354aeb4008fff85264a3c848c6c95fb8ca5b07a