Include libusb.h when using libftdi1.

libftdi1 originally included libusb.h for us in their header; they have since
cleaned this up, requiring us to do it explicitly.

This does not affect libftdi0.

BUG=None
TEST=Succesfully compiled against both old and new libftdis.

Change-Id: I1e4b3c2859191b02e2fe1922045f30dc1c3d36da
Reviewed-on: https://gerrit.chromium.org/gerrit/41654
Commit-Queue: David Schneider <dnschneid@chromium.org>
Reviewed-by: David Schneider <dnschneid@chromium.org>
Tested-by: David Schneider <dnschneid@chromium.org>
1 file changed