power: qpnp-charger: fix a variable uninitialized bug in ovp monitor

Commit 'c00e21ae' 'power: qpnp-charger: add charger OVP status
monitor' introduces a bug in 'qpnp_chg_usb_usbin_valid_irq_handler',
when 'usbin_health' value is not equal to 'USBIN_OVP' or 'USBIN_OK',
'psy_health_sts' will be used before initialized, this makes 'usb_phy'
change to an uncertain health state.

Change-Id: I95d7b119fc965afe957702e255fc376729e18856
Signed-off-by: Wu Fenglin <fenglinw@codeaurora.org>