i2c: cht-wc: Use generic_handle_irq_safe().

Instead of manually disabling interrupts before invoking use
generic_handle_irq_safe() which can be invoked with enabled and disabled
interrupts.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Wolfram Sang <wsa@kernel.org>
Signed-off-by: Wolfram Sang <wsa@kernel.org>