usb: dwc3-msm: Fix usage of find_matching_dbm_ep()

Since there is no longer an endless flag in struct usb_ep,
we simply allow some DBM specific functions to be called
unconditionally, expecting find_matching_dbm_ep() to succeed
only if it was set up to be a DBM endpoint. Thus in non-DBM
cases it is expected to return -ENODEV, which we can just
return directly and fail silently without an error message.

Change-Id: Idc3d2fc5c00f8149baec4c17872b99c3bd96665b
Signed-off-by: Jack Pham <jackp@codeaurora.org>