usb: otg: Do not call runtime suspend from system suspend callback

According to the commit text of "PM: Limit race conditions between
runtime PM and system sleep (v2)", a driver should not call
pm_runtime_suspend() from its .suspend() callback, as that creates
a recursive call into the subsystem.

This fixes msm_otg_pm_suspend() from doing just that. Instead, call
the helper function to explicitly suspend, without depending on the
runtime PM call. Likewise, the system resume callback should actually
resume the device.

Change-Id: I6ef0609dc4979ad31ef338e1eee3d21af47c256b
Signed-off-by: Jack Pham <jackp@codeaurora.org>