Fix for uhid_event size check

The uhid_event function used to expect that the return value of each
read function call to match with the size of the struct uhid_event.
Since the header file doesn't match the kernel driver, these two size
don't always match. The exact size check is replaced with expecting
the minimum required size.

Bug: 20108348
Change-Id: Ib61537092b109296f8290d802b68fc2efe78888c