iommufd: update outdated comment for renamed iommufd_hw_pagetable_alloc()

The function iommufd_hw_pagetable_alloc() was renamed to
iommufd_hwpt_paging_alloc() by commit 89db316
("iommufd: Derive iommufd_hwpt_paging from
iommufd_hw_pagetable").  Update the stale reference in
iommufd_device_auto_get_domain().

Link: https://patch.msgid.link/r/20260321105759.6832-1-kexinsun@smail.nju.edu.cn
Assisted-by: unnamed:deepseek-v3.2 coccinelle
Signed-off-by: Kexin Sun <kexinsun@smail.nju.edu.cn>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

Author: Kexin Sun

drivers/iommu/iommufd/device.c

@@ -866,7 +866,7 @@ iommufd_device_auto_get_domain(struct iommufd_device *idev, ioasid_t pasid,
 {
 	/*
 	 * iommufd_hw_pagetable_attach() is called by
-	 * iommufd_hw_pagetable_alloc() in immediate attachment mode, same as
+	 * iommufd_hwpt_paging_alloc() in immediate attachment mode, same as
 	 * iommufd_device_do_attach(). So if we are in this mode then we prefer
 	 * to use the immediate_attach path as it supports drivers that can't
 	 * directly allocate a domain.