gunzip.c: use block layer for writes

Call blk_dwrite to ensure that the block cache is notified
if enabled and remove build breakage when CONFIG_BLK is enabled.

Signed-off-by: Eric Nelson <eric@nelint.com>
Reviewed-by: Stephen Warren <swarren@nvidia.com>

lib/gunzip.c

@@ -232,9 +232,8 @@ int gzwrite(unsigned char *src, int len,
 			gzwrite_progress(iteration++,
 					 totalfilled,
 					 szexpected);
-			blocks_written = dev->block_write(dev, outblock,
-							  writeblocks,
-							  writebuf);
+			blocks_written = blk_dwrite(dev, outblock,
+						    writeblocks, writebuf);
 			outblock += blocks_written;
 			if (ctrlc()) {
 				puts("abort\n");