[nvptx, testsuite] Fix typo in gcc.target/nvptx/march.c

[nvptx, testsuite] Fix typo in gcc.target/nvptx/march.c

The dg-options line in gcc.target/nvptx/march.c:
...
/* { dg-options "-march=sm_30"} */
...
currently doesn't have any effect because it's missing a space between '"' and
'}'.

Fix this by adding the missing space.

Tested on nvptx.

gcc/testsuite/ChangeLog:

2022-03-31  Tom de Vries  <tdevries@suse.de>

	* gcc.target/nvptx/march.c: Add missing space in dg-options line.