selftests/powerpc: Fix usage message in context_switch

When we inverted the behaviour of the flags we forgot to update the
usage message.

Fixes: 51c21e72eb ("selftests/powerpc: Make context_switch touch FP/altivec/vector by default")
Signed-off-by: Cyril Bur <cyrilbur@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

tools/testing/selftests/powerpc/benchmarks/context_switch.c

@@ -369,11 +369,11 @@ static void usage(void)
 	fprintf(stderr, "\t\t--process\tUse processes (default threads)\n");
 	fprintf(stderr, "\t\t--timeout=X\tDuration in seconds to run (default 30)\n");
 	fprintf(stderr, "\t\t--vdso\t\ttouch VDSO\n");
-	fprintf(stderr, "\t\t--fp\t\ttouch FP\n");
+	fprintf(stderr, "\t\t--no-fp\t\tDon't touch FP\n");
 #ifdef __powerpc__
-	fprintf(stderr, "\t\t--altivec\ttouch altivec\n");
+	fprintf(stderr, "\t\t--no-altivec\tDon't touch altivec\n");
 #endif
-	fprintf(stderr, "\t\t--vector\ttouch vector\n");
+	fprintf(stderr, "\t\t--no-vector\tDon't touch vector\n");
 }
 
 int main(int argc, char *argv[])