HID: Do not discard truncated input reports

Truncated reports should not be discarded since it prevents buggy
devices from communicating with userspace.

Prior to the regession introduced in 2.6.20, a shorter-than-expected
report in hid_input_report() was passed thru after having the missing
bytes cleared. This behavior was established over a few patches in the
2.6.early-teens days, including commit
cd6104572bca9e4afe0dcdb8ecd65ef90b01297b.

This patch restores the previous behavior and fixes the regression.

Signed-off-by: Adam Kropelin <akropel1@rochester.rr.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>