usbatm_heavy_init: don't use CLONE_SIGHAND

usbatm_do_heavy_init() calls allow_signal() which plays with parent process's
->sighand.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Acked-by: Duncan Sands <duncan.sands@free.fr>
Cc: Greg KH <greg@kroah.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>