powerpc: Fix a kernel-doc warning

The current code provokes a kernel-doc warnings:
  arch/powerpc/kernel/process.c:1606: warning: This comment starts with
  '/**', but isn't a kernel-doc comment. Refer
  Documentation/doc-guide/kernel-doc.rst
Signed-off-by: Bo Liu <liubo03@inspur.com>
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20221101015452.3216-1-liubo03@inspur.com

arch/powerpc/kernel/process.c

@@ -1630,7 +1630,7 @@ void arch_setup_new_exec(void)
 }
 
 #ifdef CONFIG_PPC64
-/**
+/*
  * Assign a TIDR (thread ID) for task @t and set it in the thread
  * structure. For now, we only support setting TIDR for 'current' task.
  *