dwc3: fix snps,dis-del-phy-power-chg-quirk

If snps,dis-del-phy-power-chg-quirk is set, the register bit should be
cleared not ored on (it's the "dis" version).

Reviewed by: mw
Differential Revision: https://reviews.freebsd.org/D35697

(cherry picked from commit 0084212bfdfbcd662f3e823636b40173e828509d)