powerpc: Fix lwsync patching code on 64bit

do_lwsync_fixups doesn't work on 64bit, we end up writing lwsyncs to the
wrong addresses:

0:mon> di c0000001000bfacc
c0000001000bfacc  7c2004ac      lwsync

Since the lwsync section has negative offsets we need to use a signed int
pointer so we sign extend the value.
Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/lib/feature-fixups.c

@@ -112,7 +112,7 @@ void do_feature_fixups(unsigned long value, void *fixup_start, void *fixup_end)
 
 void do_lwsync_fixups(unsigned long value, void *fixup_start, void *fixup_end)
 {
-	unsigned int *start, *end, *dest;
+	int *start, *end, *dest;
 
 	if (!(value & CPU_FTR_LWSYNC))
 		return ;