hwclock: use a consistent name for --predict

hwclock: use a consistent name for --predict

The predict function name is documented as '--predict', but the
code uses '--predict-hc'. This works okay, except that the
'mutually exclusive' error message prints the undocumented name.

* sys-utils/hwclock.c: rename 'predict-hc' to 'predict' so that
    it matches the man-page. This should not be a problem because
    'predict-hc' was never documented.

Signed-off-by: J William Piggott <elseifthen@gmx.com>