usb: f_gsi: Increase GPS EP maxpacket size to 64bytes

Currently usb driver is using 8 bytes request on interrupt endpoint
for all CDC functions. GPS host driver is expecting short packet/zero
length packet on interrupt endpoint and failing the transfer with 8 bytes
maxpacket. Increase the maxpacket size to 64 bytes so that host ends
the transfer with a short packet.

Change-Id: Icc9919fbd633468d3cc7d4d8ab1945730cdc7c06
Signed-off-by: Chandana Kishori Chiluveru <cchiluve@codeaurora.org>