RFR(trivial): 8217417: Decorator name typo: C2_TIGHLY_COUPLED_ALLOC

[Kim Barrett]

Please review this trivial fix of a typo in a decorator name that has
propagated a bit.

CR:
https://bugs.openjdk.java.net/browse/JDK-8217417

Webrev:
http://cr.openjdk.java.net/~kbarrett/8217417/open.00/

Testing:
mach5 build on Oracle supported platforms.
local (linux-x64-debug) build with shenandoah enabled, since on of the
propagated typos is there.