dwc3-msm: Add missing enum related value with gsi_op_strings array

GSI_EP_OP_GET_XFER_IDX enum related value is missing with table
causing different gsi endpoint operation related information in debug
log instead of expected. Hence fix this issue by adding "GET_XFER_IDX"
value as correct index with gsi_op_strings array.

Change-Id: I30c2a6b643d747c68f5e524db8680580501aeaef
Signed-off-by: Mayank Rana <mrana@codeaurora.org>