checkpatch: add __pmem to $Sparse annotations

checkpatch: add __pmem to $Sparse annotations

Orabug: 22913653

commit 61031952f4c8 ("arch, x86: pmem api for ensuring durability of
persistent memory updates") added a new __pmem annotation for sparse
verification.  Add __pmem to the $Sparse variable so checkpatch can
appropriately ignore uses of this attribute too.

Signed-off-by: Joe Perches <joe@perches.com>
Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Acked-by: Andy Whitcroft <apw@canonical.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
(cherry picked from commit 54507b5183cc4f8e4f1a58a312e1f30c130658b7)
Signed-off-by: Dan Duval <dan.duval@oracle.com>