mm, hugetlb: change variable name reservations to resv

mm, hugetlb: change variable name reservations to resv

'reservations' is so long name as a variable and we use 'resv_map' to
represent 'struct resv_map' in other place.  To reduce confusion and
unreadability, change it.

Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Reviewed-by: Aneesh Kumar <aneesh.kumar@linux.vnet.ibm.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Reviewed-by: Davidlohr Bueso <davidlohr@hp.com>
Cc: David Gibson <david@gibson.dropbear.id.au>
Cc: Wanpeng Li <liwanp@linux.vnet.ibm.com>
Cc: Hillf Danton <dhillf@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
(cherry picked from commit f522c3ac00a49128115f99a5fcb95a447601c1c3)
Signed-off-by: Mark Brown <broonie@linaro.org>