usb: dwc2: gadget: Expand buffer size of control endpoint

usb: dwc2: gadget: Expand buffer size of control endpoint

We found the case that buffer of control endpoint, which was allocated
with 8 bytes previously, is corrupted when the host races for setting
up interfaces. Even worse, it overwrites memory for other structure
such as usb_request for control endpoint and it causes kernel panic.
Especially in Tizen, it often happens when the target is configured as
multi-functional device: sdb + mtp.

In our emprical examination the buffer can be corrupted upto size of
456 bytes. With this result, the size of buffer will be enlarged to
512 bytes to prevent kernel panic even if it happens.

Change-Id: I20eb1283f3c82e09453960b72787175f734e7ec4
Signed-off-by: Seung-Woo Kim <sw0312.kim@samsung.com>
Signed-off-by: Dongwoo Lee <dwoo08.lee@samsung.com>