ANDROID: GKI: fix up mhi.ko build location.

In commit 9fbf1014 ("bus: mhi: Move host MHI code to "host"
directory"), the mhi.ko module moved directories, which breaks the build
of the db845c target in the Android TH testing environment.  Update the
BUILD.bazel file with the new location of the kernel module.

Fixes: 9fbf1014 ("bus: mhi: Move host MHI code to "host" directory")
Change-Id: Ib39224dc50055b22d58a27eeb60948ae67b637b0
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>