remove a useless volatile
remove a useless volatile

... introduced with 8c113ff64b78554f6219f14774fed418c466318c

Here it seems the intention was to make sure that the access to the
parameter happens uncached, but even then it would not have helped.

gquintard/Varnish-Cache,gquintard/Varnish-Cache,gquintard/Varnish-Cache,gquintard/Varnish-Cache