Fix slab name "biovec-(1<<(21-12))"

Fix slab name "biovec-(1<<(21-12))"

BugLink: http://bugs.launchpad.net/bugs/1762370
commit bd5c4facf59648581d2f1692dad7b107bf429954 upstream.

I'm getting a slab named "biovec-(1<<(21-12))". It is caused by unintended
expansion of the macro BIO_MAX_PAGES. This patch renames it to biovec-max.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Cc: stable@vger.kernel.org	# v4.14+
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>