powerpc/rtas: Fix ppc_rtas_rmo_buf_show() kernel-doc

>From a W=1 build:

>> arch/powerpc/kernel/rtas-proc.c:771: warning: Function parameter or member 'm' not described in
>> 'ppc_rtas_rmo_buf_show'
>> arch/powerpc/kernel/rtas-proc.c:771: warning: Function parameter or member 'v' not described in
>> 'ppc_rtas_rmo_buf_show'

Add the missing parameter descriptions.

Signed-off-by: Nathan Lynch <nathanl@linux.ibm.com>
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202309211645.1Lvwmbv4-lkp@intel.com/


Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20231106-rtas-trivial-v1-2-61847655c51f@linux.ibm.com