mm: do_mincore() cleanup

Two cleanups:
1. remove redundant codes for hugetlb pages.
2. end = pmd_addr_end(addr, end) restricts [addr, end) within PMD_SIZE,
   this may increase do_mincore() calls, remove it.

Signed-off-by: Jianguo Wu <wujianguo@huawei.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Minchan Kim <minchan.kim@gmail.com>
Cc: qiuxishi <qiuxishi@huawei.com>
Reviewed-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>