usb: dwc3: msm: rename lpm_irq_seen flag

Changing the name of the flag used to indicate that the
hs_phy_irq was triggered. This is done in order to provide
more clarity, as the pwr_event_irq can also be indicative
of lpm.

Change-Id: I31e2e8e38b608f19356608615f9d97b8059315bf
Signed-off-by: Bar Weiner <bweiner@codeaurora.org>