hugetlb: debit quota in alloc_huge_page

Now that quota is credited by free_huge_page(), calls to hugetlb_get_quota()
seem out of place.  The alloc/free API is unbalanced because we handle the
hugetlb_put_quota() but expect the caller to open-code hugetlb_get_quota().
Move the get inside alloc_huge_page to clean up this disparity.

This patch has been kept apart from the previous patch because of the somewhat
dodgy ERR_PTR() use herein.  Moving the quota logic means that
alloc_huge_page() has two failure modes.  Quota failure must result in a
SIGBUS while a standard allocation failure is OOM.  Unfortunately, ERR_PTR()
doesn't like the small positive errnos we have in VM_FAULT_* so they must be
negated before they are used.

Does anyone take issue with the way I am using PTR_ERR.  If so, what are your
thoughts on how to clean this up (without needing an if,else if,else block at
each alloc_huge_page() callsite)?

Signed-off-by: Adam Litke <agl@us.ibm.com>
Cc: Ken Chen <kenchen@google.com>
Cc: Andy Whitcroft <apw@shadowen.org>
Cc: Dave Hansen <haveblue@us.ibm.com>
Cc: David Gibson <hermes@gibson.dropbear.id.au>
Cc: William Lee Irwin III <wli@holomorphy.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>