zram: don't pass a bvec to __zram_bvec_write

__zram_bvec_write only extracts the page from __zram_bvec_write and always
expects a full page of input.  Pass the page directly instead of the bvec
and rename the function to zram_write_page.

Link: https://lkml.kernel.org/r/20230411171459.567614-13-hch@lst.de


Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>