block/bio: Do not zero user pages

BugLink: http://bugs.launchpad.net/bugs/1834499
We don't need to zero fill the bio if not using kernel allocated pages.

Fixes: f3587d76da05 ("block: Clear kernel memory before copying to user") # v4.20-rc2
Reported-by: Todd Aiken <taiken@mvtech.ca>
Cc: Laurence Oberman <loberman@redhat.com>
Cc: stable@vger.kernel.org
Cc: Bart Van Assche <bvanassche@acm.org>
Tested-by: Laurence Oberman <loberman@redhat.com>
Signed-off-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
(cherry picked from commit f55adad601c6a97c8c9628195453e0fb23b4a0ae)
Signed-off-by: Marcelo Henrique Cerri <marcelo.cerri@canonical.com>
Acked-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Acked-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>