f_sdp: Fix wrong usb request size

Because the buffer length of sdp usb request is 65, we have to allocate
65 bytes not 64 bytes. Otherwise there is potential buffer overflow.

Signed-off-by: Ye Li <ye.li@nxp.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>
Reviewed-by: Lukasz Majewski <lukma@denx.de>