Fix 'libgomp.fortran/reverse-offload-6.f90' nvptx offloading compilation

Fix-up for recent commit 0b1ce70a813b98ef2893779d14ad6c90c5d06a71
"libgomp: Fix reverse offload issues".

	libgomp/
	* testsuite/libgomp.fortran/reverse-offload-6.f90: Fix nvptx
	offloading compilation.
diff --git a/libgomp/testsuite/libgomp.fortran/reverse-offload-6.f90 b/libgomp/testsuite/libgomp.fortran/reverse-offload-6.f90
index 04866ed..ddb7008 100644
--- a/libgomp/testsuite/libgomp.fortran/reverse-offload-6.f90
+++ b/libgomp/testsuite/libgomp.fortran/reverse-offload-6.f90
@@ -2,6 +2,8 @@
 ! Ensure that a mapping with no argument works
 !
 
+! { dg-additional-options -foffload-options=nvptx-none=-misa=sm_35 { target offload_target_nvptx } }
+
 module m
   implicit none (type, external)
   integer :: x = 32