[nvptx, testsuite] Add -misa=sm_30 in nvptx/uniform-simt-2.c

[nvptx, testsuite] Add -misa=sm_30 in nvptx/uniform-simt-2.c

When running with target board nvptx-none-run/-misa=sm_53 we run into:
...
cc1: error: PTX version (-mptx) needs to be at least 4.2 to support selected \
  -misa (sm_53)^M
compiler exited with status 1
FAIL: gcc.target/nvptx/uniform-simt-2.c (test for excess errors)
...

Fix this by adding an explicit -misa=sm_30 in the test-case.

Tested on nvptx.

gcc/testsuite/ChangeLog:

2022-02-28  Tom de Vries  <tdevries@suse.de>

	* gcc.target/nvptx/uniform-simt-2.c: Add -misa=sm_30.