drivers:block: cpqarray clean up

Commit d4366414 ("cpqarray: remove it from the kernel") removes the
Kconfig option BLK_CPQ_DA and cpqarray.

Remove the dead build rule in the Makefile.

Signed-off-by: Valentin Rothberg <valentinrothberg@gmail.com>
Signed-off-by: Jens Axboe <axboe@fb.com>