Fix up 'g++.dg/abi/nvptx-ptrmem1.C'

..., which shortly after its inception in
commit 44eba92d (Subversion r231628)
"[PTX] parameters and return values" was forgotten to be updated in next day's
commit 1f065954 (Subversion r231663)
"[PTX] more register cleanups".  Fix it up now, as obvious, for the current
state of things.

	gcc/testsuite/
	* g++.dg/abi/nvptx-ptrmem1.C: Fix up.