tools/mm/slabinfo: fix --partial long option mapping

tools/mm/slabinfo: fix --partial long option mapping

The long option "--partial" was incorrectly mapped to lowercase 'p' in the
opts[] array, but the getopt string and switch case handle uppercase 'P'.
This mismatch caused --partial to be rejected.

Fix the long_options mapping to use 'P' so --partial works correctly
alongside the existing -P short option.

Link: https://lkml.kernel.org/r/20251208105240.2719773-1-kaushlendra.kumar@intel.com
Signed-off-by: Kaushlendra Kumar <kaushlendra.kumar@intel.com>
Reviewed-by: SeongJae Park <sj@kernel.org>
Tested-by: SeongJae Park <sj@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>