[NVPTX][test] fixup version for ptxas on trunc-tofp.ll (#149558)

Author: AlexMaclean

llvm/test/CodeGen/NVPTX/trunc-tofp.ll

@@ -1,6 +1,6 @@
 ; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 5
-; RUN: llc < %s -mcpu=sm_80 | FileCheck %s
-; RUN: %if ptxas %{ llc < %s -mcpu=sm_80 | %ptxas-verify %}
+; RUN: llc < %s -mcpu=sm_50 | FileCheck %s
+; RUN: %if ptxas %{ llc < %s -mcpu=sm_50 | %ptxas-verify -arch=sm_50 %}
 
 target triple = "nvptx64-nvidia-cuda"