USB: gadget: Clear csw_hack_sent flag during fsg_set_alt

Even after cable disconnect, csw_hack_sent flag might be
still set in some corner cases. If set, it leads to CSW
not being sent to Host for next cable connect or usb
composition switch in superspeed mode. This results in
reset being sent by Host and could cause reenumeration.
Hence fix this issue by clearing csw_hack_sent flag
in fsg_set_alt call for next connect.

CRs-Fixed: 438647
Change-Id: I8b15e90a1dbed7c08bff401a54dce817c8748af1
Signed-off-by: Vijayavardhan Vennapusa <vvreddy@codeaurora.org>
Signed-off-by: Tarun Gupta <tarung@codeaurora.org>