Input: ims-pcu - validate number of endpoints before using them

Make sure to check the number of endpoints to avoid dereferencing a
NULL-pointer should a malicious device lack control-interface endpoints.

Fixes: 628329d5

 ("Input: add IMS Passenger Control Unit driver")
Signed-off-by: Johan Hovold <johan@kernel.org>
Cc: stable@vger.kernel.org	# 3.10
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>