5255 uts shouldn't open-code ISP2

@@ -3785,11 +3785,11 @@
         }
 
         hdr = kobj_comphdr(file);
         if (hdr->ch_magic != CH_MAGIC_ZLIB || hdr->ch_version != CH_VERSION ||
             hdr->ch_algorithm != CH_ALG_ZLIB || hdr->ch_fsize == 0 ||
-            (hdr->ch_blksize & (hdr->ch_blksize - 1)) != 0) {
+            !ISP2(hdr->ch_blksize)) {
                 kobj_free(file->_dbuf, cip->fsize);
                 return (-1);
         }
         file->_base = kobj_alloc(hdr->ch_blksize, KM_WAIT|KM_TMP);
         file->_bsize = hdr->ch_blksize;