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 <[email protected]>
Reviewed-by: Aneesh Kumar <[email protected]>
Cc: Naoya Horiguchi <[email protected]>
Reviewed-by: Davidlohr Bueso <[email protected]>
Cc: David Gibson <[email protected]>
Cc: Wanpeng Li <[email protected]>
Cc: Hillf Danton <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>