usb: dwc3: remove LPM L2 OUT interrupt

when LPM L2 OUT interrupt happen, need to clear state bit for new,
but there is issue for old code: irq_stat |= PWR_EVNT_LPM_OUT_L2_MASK;,
acctually it should be: irq_clear |= PWR_EVNT_LPM_OUT_L2_MASK;,
old code do nothing, it just test bit -> clear bit --> set bit,
remove old code will keep old behaviour.

Change-Id: Ib5938a31df69793c3b21914777ff0e0ac11be59d
Signed-off-by: Linyu Yuan <linyyuan@codeaurora.org>