powerpc/pseries/rtas-work-area: Fix rtas_work_area_reserve_arena() kernel-doc

>From a W=1 build:

>> arch/powerpc/platforms/pseries/rtas-work-area.c:189: warning: Function parameter or member 'limit' not
>> described in 'rtas_work_area_reserve_arena'

Add the missing description of the limit parameter.
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/202309131221.Bm1pg96n-lkp@intel.com/Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20231106-rtas-trivial-v1-1-61847655c51f@linux.ibm.com

arch/powerpc/platforms/pseries/rtas-work-area.c

@@ -184,6 +184,7 @@ machine_arch_initcall(pseries, rtas_work_area_allocator_init);
 
 /**
  * rtas_work_area_reserve_arena() - Reserve memory suitable for RTAS work areas.
+ * @limit: Upper limit for memblock allocation.
  */
 void __init rtas_work_area_reserve_arena(const phys_addr_t limit)
 {