usb: gadget: Use mult as 3 for GSI related USB IN endpoint always

Interfaces like MBIM or ECM is having multiple data interfaces.
In this case, SET_CONFIG() happens before set_alt with data interface 1.
Due to this, TXFIFO of GSI IN endpoint is not resized causing low
throughput in DL direction. Fix this issue by using mult as 3 for
GSI related USB IN endpoint irrespective of super-speed or high-speed
mode.

CRs-Fixed: 1025031
Change-Id: I10de98ae57284699af3abcd90bafac63ba03844e
Signed-off-by: Mayank Rana <mrana@codeaurora.org>