max1720x_battery: release model_lock before max1720x_fg_irq_thread_fn

The model_lock was held in max1720x_fg_irq_thread_fn
->max1720x_model_reload.
Need to release model_lock before holding it again.

Bug: 202520235
Signed-off-by: Jenny Ho <hsiufangho@google.com>
Change-Id: Ie7701dd55cadb60d717491b2b9654d926b0cf6dc