USB: f_diag: Report Max request size as 16k for ChipIdea

ChipIdea controller can be queued a maximum packet size of 16KB.
If a request larger than this size arrives on IN endpoint,
request is failed. Fix this by limiting the max request size to
16k if the controller is ChipIdea.

Change-Id: Iac696addc9b1ca50e78ae66f73f5b66bd3100c1c
Signed-off-by: Ajay Agarwal <ajaya@codeaurora.org>