powerpc: Use WARN_ON(1) instead of __WARN()

__WARN() is not defined for all configs, use WARN_ON(1) instead.
Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/lib/feature-fixups.c

@@ -99,7 +99,7 @@ void do_feature_fixups(unsigned long value, void *fixup_start, void *fixup_end)
 
 	for (; fcur < fend; fcur++) {
 		if (patch_feature_section(value, fcur)) {
-			__WARN();
+			WARN_ON(1);
 			printk("Unable to patch feature section at %p - %p" \
 				" with %p - %p\n",
 				calc_addr(fcur, fcur->start_off),