powerpc/powermac: Fix unused function warning

Clang reports:
  arch/powerpc/platforms/powermac/feature.c:137:19: error: unused function 'simple_feature_tweak'

It's only used inside the #ifndef CONFIG_PPC64 block, so move it in
there to fix the warning. While at it drop the inline, the compiler will
decide whether it should be inlined or not.
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202308181501.AR5HMDWC-lkp@intel.com/Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230821140949.491881-1-mpe@ellerman.id.au

arch/powerpc/platforms/powermac/feature.c

@@ -134,8 +134,10 @@ static struct pmac_mb_def pmac_mb;
  * Here are the chip specific feature functions
  */
 
-static inline int simple_feature_tweak(struct device_node *node, int type,
-				       int reg, u32 mask, int value)
+#ifndef CONFIG_PPC64
+
+static int simple_feature_tweak(struct device_node *node, int type, int reg,
+				u32 mask, int value)
 {
 	struct macio_chip*	macio;
 	unsigned long		flags;
@@ -154,8 +156,6 @@ static inline int simple_feature_tweak(struct device_node *node, int type,
 	return 0;
 }
 
-#ifndef CONFIG_PPC64
-
 static long ohare_htw_scc_enable(struct device_node *node, long param,
 				 long value)
 {