powerpc/pseries: PLPKS: undo kernel-doc comment notation

Don't use kernel-doc "/**" comment format for non-kernel-doc comments.
This prevents a kernel-doc warning:

  arch/powerpc/platforms/pseries/plpks.c:186: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
  * Label is combination of label attributes + name.

Fixes: 2454a7af ("powerpc/pseries: define driver for Platform KeyStore")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Reported-by: kernel test robot <lkp@intel.com>
Link: lore.kernel.org/r/202308040430.GxmPAnwZ-lkp@intel.com
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230810000740.23756-1-rdunlap@infradead.org