powerpc: Use sizeof(struct thread_info) in INIT_SP_LIMIT

Currently INIT_SP_LIMIT uses sizeof(init_thread_info), but that symbol
won't exist when we enable THREAD_INFO_IN_TASK. So just use the sizeof
the type which is the same value but will continue to work.
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
[mpe: Split out of larger patch]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/processor.h

@@ -271,7 +271,7 @@ struct thread_struct {
 
 #define INIT_SP		(sizeof(init_stack) + (unsigned long) &init_stack)
 #define INIT_SP_LIMIT \
-	(_ALIGN_UP(sizeof(init_thread_info), 16) + (unsigned long) &init_stack)
+	(_ALIGN_UP(sizeof(struct thread_info), 16) + (unsigned long)&init_stack)
 
 #ifdef CONFIG_SPE
 #define SPEFSCR_INIT \