InputDevice: clear absolute axis info if not found

In change I57de645c889de53c8be0f9f8744a62e92fafdadb, getAbsoluteAxisInfo
was modified to handle EventHub::getAbsoluteAxisInfo returning an
optional. However, the old form of EventHub::getAbsoluteAxisInfo had the
side effect of clearing the RawAbsoluteAxisInfo struct that it was
passed a pointer to if the axis isn't present, crucially setting valid
to false. To avoid a behaviour change due to the refactor, mimic that in
InputDevice::getAbsoluteAxisInfo.

Test: atest inputflinger_tests
Test: m checkinput
Bug: 245989146
Flag: EXEMPT refactor
Change-Id: If32272f983139c2e9d5f1e548fb209c21d191180