mfd: omap-usb-host: Fix improper mask use.

single-ulpi-bypass is a flag used for older OMAP3 silicon.

The flag when set, can excite code that improperly uses the
OMAP_UHH_HOSTCONFIG_UPLI_BYPASS define to clear the corresponding bit.
Instead it clears all of the other bits disabling all of the ports in
the process.

Cc: stable@vger.kernel.org
Signed-off-by: Michael Welling <mwelling@emacinc.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>