zram: clarify writeback_store() comment

Re-phrase writeback BIO error comment.

Link: https://lkml.kernel.org/r/[e-mail]
Reported-by: Andrew Morton <[e-mail]>
Signed-off-by: Sergey Senozhatsky <[e-mail]>
Acked-by: Minchan Kim <[e-mail]>
Cc: Alexey Romanov <[e-mail]>
Cc: Nhat Pham <[e-mail]>
Cc: Nitin Gupta <[e-mail]>
Cc: Suleiman Souhlal <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

drivers/block/zram/zram_drv.c

···
 			zram_clear_flag(zram, index, ZRAM_IDLE);
 			zram_slot_unlock(zram, index);
 			/*
-			 * Return last IO error unless every IO were
-			 * not suceeded.
+			 * BIO errors are not fatal, we continue and simply
+			 * attempt to writeback the remaining objects (pages).
+			 * At the same time we need to signal user-space that
+			 * some writes (at least one, but also could be all of
+			 * them) were not successful and we do so by returning
+			 * the most recent BIO error.
 			 */
 			ret = err;
 			continue;