staging: vchiq_core: remove BITSET_ZERO

Hiding memset behind a macro isn't the best, because it relies on that
the parameter is not a pointer. Luckily all user has been removed, so
we can remove BITSET_ZERO too.

Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>