pegasus: Use heap buffers for all register access

commit 5593523f968bc86d42a035c6df47d5e0979b5ace upstream.

Allocating USB buffers on the stack is not portable, and no longer
works on x86_64 (with VMAP_STACK enabled as per default).

Fixes: 1da177e4 ("Linux-2.6.12-rc2")
References: https://bugs.debian.org/852556


Reported-by: Lisandro Damián Nicanor Pérez Meyer <lisandro@debian.org>
Tested-by: Lisandro Damián Nicanor Pérez Meyer <lisandro@debian.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>
Cc: Brad Spengler <spender@grsecurity.net>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Willy Tarreau <w@1wt.eu>