powerpc/process: Tag an #endif to help locate the matching #ifdef.

That #endif is more than 100 lines after the matching #ifdef,
and there are several #ifdef/#else/#endif inbetween.

Tag it as /* CONFIG_PPC_BOOK3S_64 */ to help locate the
matching #ifdef.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/3612a8f8aaca16de3fc414a7e66293319d6e213c.1597643147.git.christophe.leroy@csgroup.eu

arch/powerpc/kernel/process.c

@@ -581,7 +581,7 @@ void notrace restore_math(struct pt_regs *regs)
 		regs->msr |= new_msr | fpexc_mode;
 	}
 }
-#endif
+#endif /* CONFIG_PPC_BOOK3S_64 */
 
 static void save_all(struct task_struct *tsk)
 {