f_gsi: Correct string descriptor value of DPL interface

Correct string descriptor value from "QDSS Data" to "Qualcomm DPL Data"
as some of host side application looks for specific value with string
descriptor to detect enumerated device and allow IO with it. Hence
correct string descriptor value of DPL interface.

Change-Id: I938668223c5c4fb669830c4ad8ab26161b6d56a7
Signed-off-by: Mayank Rana <mrana@codeaurora.org>