tests/drv_suspend: Replace "&> /dev/null" with "> /dev/null 2>&1"

tests/drv_suspend: Replace "&> /dev/null" with "> /dev/null 2>&1"

Some shells do not understand "&>". For instance, my Ubuntu 12.04
machine has /bin/sh pointing to dash, which makes a mess out of
"&>" (to the point that the helper processes cannot be killed).

Reviewed-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Oscar Mateo <oscar.mateo@intel.com>
Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>