powerpc/kasan: Fix shadow start address with modules

Modules are now located before kernel, KASAN area has to
be extended accordingly.

Fixes: 80edc68e ("powerpc/32s: Define a MODULE area below kernel text all the time")
Fixes: 9132a2e8 ("powerpc/8xx: Define a MODULE area below kernel text")
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/c68163065163f303f5af1e4bbdd9f1ce69f0543e.1619260465.git.christophe.leroy@csgroup.eu

arch/powerpc/include/asm/kasan.h

@@ -19,7 +19,7 @@
 
 #define KASAN_SHADOW_SCALE_SHIFT	3
 
-#if defined(CONFIG_PPC_BOOK3S_32) && defined(CONFIG_MODULES) && defined(CONFIG_STRICT_KERNEL_RWX)
+#ifdef CONFIG_MODULES
 #define KASAN_KERN_START	ALIGN_DOWN(PAGE_OFFSET - SZ_256M, SZ_256M)
 #else
 #define KASAN_KERN_START	PAGE_OFFSET