HID: wacom: fix timeout on probe for some wacoms

Some Wacom tablets (at least the ISDv4 found in the Lenovo X230) timeout
during probe while retrieving the input reports.
The only time this information is valuable is during the feature_mapping
stage, so we can ask for it there and discard the generic input reports
retrieval.

This gives a code path closer to the wacom.ko driver when it was in the
input subtree (not HID).

Cc: stable@vger.kernel.org # requires cherry-pick of c64d8834
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>