recovery: fix another misspelling of "file_blocks" as "block_size"

Together with I1efff752a223cc937c3a9e3b6a994545a5696379, this makes it
possible to install small (file_blocks < block_size) updates without
getting mysterious bus errors.

Change-Id: I49df1bcc4615d59bd00678df5765f054ccce6522
Signed-off-by: Michael Livshin <michael@cellrox.com>

fuse_sideload.c

@@ -149,7 +149,7 @@ static void block_cache_enter(struct fuse_data* fd, uint32_t block)
         int n;
         for (n = fd->curr_block - 1; n != (int)fd->curr_block; --n) {
             if (n < 0) {
-                n = fd->block_size - 1;
+                n = fd->file_blocks - 1;
             }
             if (fd->block_cache[n]) {
                 free(fd->block_cache[n]);