usb: gadget: eem: fix wrong eem header operation

commit 305f6708

 upstream.

when skb_clone() or skb_copy_expand() fail,
it should pull skb with lengh indicated by header,
or not it will read network data and check it as header.

Cc: <stable@vger.kernel.org>
Signed-off-by: Linyu Yuan <linyyuan@codeaurora.com>
Link: https://lore.kernel.org/r/20210608233547.3767-1-linyyuan@codeaurora.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>