zram: avoid double free in function zram_bvec_write()

When doing a patial write and the whole page is filled with zero,
zram_bvec_write() will free uncmem twice.

Signed-off-by: Jiang Liu <jiang.liu@huawei.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/zram/zram_drv.c

@@ -272,8 +272,6 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
 
 	if (page_zero_filled(uncmem)) {
 		kunmap_atomic(user_mem);
-		if (is_partial_io(bvec))
-			kfree(uncmem);
 		zram->stats.pages_zero++;
 		zram_set_flag(meta, index, ZRAM_ZERO);
 		ret = 0;