zram: Protect handle_decomp_fail behind a check

the previous definitions as well as the creation of this is locked behind CONFIG_ZRAM_LRU_WRITEBACK as well

Change-Id: I869b5595f69cc481e93ca6862b460594762d9b25

# Conflicts:
#	drivers/block/zram/zram_drv.c

drivers/block/zram/zram_drv.c

@@ -3026,10 +3026,12 @@ static int __zram_bvec_read(struct zram *zram, struct page *page, u32 index,
 		zcomp_stream_put(zram->comp);
 	}
 
+#ifdef CONFIG_ZRAM_LRU_WRITEBACK
 	/* Should NEVER happen. BUG() if it does. */
 	if (unlikely(ret))
 		handle_decomp_fail(zram->compressor, ret, index, src, size,
 				   NULL);
+#endif
 
 	zs_unmap_object(zram->mem_pool, zram_entry_handle(zram, entry));
 #ifdef CONFIG_ZRAM_LRU_WRITEBACK