util/disk_cache: fix compressed size calculation

It incorrectly doubles the size on each iteration.

Fixes: 85a9b1b5 "util/disk_cache: compress individual cache entries"

Signed-off-by: Grazvydas Ignotas <notasas@gmail.com>
Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>

src/util/disk_cache.c

@@ -696,7 +696,7 @@ deflate_and_write_to_disk(const void *in_data, size_t in_data_size, int dest,
          assert(ret != Z_STREAM_ERROR);  /* state not clobbered */
 
          size_t have = BUFSIZE - strm.avail_out;
-         compressed_size += compressed_size + have;
+         compressed_size += have;
 
          size_t written = 0;
          for (size_t len = 0; len < have; len += written) {