gpumon: Fix pattern match ambiguity
gpumon: Fix pattern match ambiguity

Make sure threads call register_thread. Previously this was only called
by threads entering the critical section after the first.

Signed-off-by: John Else <37b74501daa612e48fea94f9846ed4ddeb6a8f07@citrix.com>

thomassa/xen-api,euanh/xen-api,Frezzle/xen-api,rafalmiel/xen-api,euanh/xen-api,euanh/xen-api,Frezzle/xen-api,srowe/xen-api,rafalmiel/xen-api,thomassa/xen-api,Frezzle/xen-api,euanh/xen-api,thomassa/xen-api,Frezzle/xen-api,rafalmiel/xen-api,srowe/xen-api,thomassa/xen-api,euanh/xen-api,rafalmiel/xen-api,thomassa/xen-api,srowe/xen-api,rafalmiel/xen-api,rafalmiel/xen-api,Frezzle/xen-api,srowe/xen-api,euanh/xen-api,srowe/xen-api,thomassa/xen-api