hid_locate: do not ignore constant items.
hid_locate() currently ignores all HID items which tagged as constant,
i.e. bit 0 of main item data is set to 1. See p.18.104.22.168 of
hid1_11.pdf . Such an items are unconditionally treated as
byte-alignment padding. While that may be right decision for input and
output reports that is wrong for features reports. Feature reports can
contain constant capabilities e.g. 'Contact Count Maximum'.
Remove check for constant from hid_locate() to make possible parsing of
such a reports.
Reviewed by: hselasky
Obtained from: sysutils/iichid
Differential Revision: https://reviews.freebsd.org/D27747