usb: dwc3-msm: Fix potential array out-of- bounds access

Ensure bus_vote_values and mdwc->dbm_ep_num_mapping use indices
within range.

Change-Id: I9f02bfc416629ada0ed46cabb3931c6f7b0977aa
Signed-off-by: Ronak Vijay Raheja <rraheja@codeaurora.org>