zram: use memcpy_to_bvec in zram_bvec_read

Use the proper helper instead of open coding the copy.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Link: https://lore.kernel.org/r/20220303111905.321089-4-hch@lst.de


Signed-off-by: Jens Axboe <axboe@kernel.dk>