testsuite: Fix up gcc.target/powerpc/pr93122.c test

testsuite: Fix up gcc.target/powerpc/pr93122.c test

The recent renaming of PowerPC -mprefixed-addr option to -mprefixed
has not adjusted the gcc.target/powerpc/pr93122.c test, so it now
FAIL: gcc.target/powerpc/pr93122.c (test for excess errors)
Excess errors:
xgcc: error: unrecognized command-line option '-mprefixed-addr'; did you mean '-mprefixed'?

2020-02-12  Jakub Jelinek  <jakub@redhat.com>

	* gcc.target/powerpc/pr93122.c: Use -mprefixed instead of
	-mprefixed-addr in dg-options.