iova: Remove some magazine pointer NULL checks

iova: Remove some magazine pointer NULL checks

Since commit 0d5029d0a754 ("iommu/iova: Separate out rcache init") it
has not been possible to have NULL CPU rcache "loaded" or "prev" magazine
pointers once the IOVA domain has been properly initialized. Previously it
was only possible to have NULL pointers from failure to allocate the
magazines in the IOVA domain initialization. The only other two functions
to modify these pointers - __iova_rcache_{get, insert}() - would already
ensure that these pointers were non-NULL if initially non-NULL.

As such, the mag NULL pointer checks in iova_magazine_full(),
iova_magazine_empty(), and iova_magazine_free_pfns() may be dropped.

Signed-off-by: John Garry <john.garry@huawei.com>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Reviewed-by: Jerry Snitselaar <jsnitsel@redhat.com>
Link: https://lore.kernel.org/r/1662557681-145906-2-git-send-email-john.garry@huawei.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>