serial_hid: silence compiler warning (unused value)

serial_hid: silence compiler warning (unused value)

Silence a compiler warning about assigning a value to a variable that's
not used in subsequent instructions. This 'have_chip' condition is worth
keeping around, in case the HID chip search code receives updates later.
Removing the assignment may complicate maintenance, or result in
incomplete diagnostics during research.

../src/serial_hid.c:1066:3: warning: Value stored to 'have_chip' is never read
                have_chip = 1;