PCI/P2PDMA: Fix incorrect pointer usage in devm_kfree() call

PCI/P2PDMA: Fix incorrect pointer usage in devm_kfree() call

The error handling path in pci_p2pdma_add_resource() contains a bug in its
`pgmap_free` label.

Memory is allocated for the `p2p_pgmap` struct, and the pointer is stored
in `p2p_pgmap`. However, the error path calls devm_kfree() with `pgmap`,
which is a pointer to a member field within the `p2p_pgmap` struct, not the
base pointer of the allocation.

Correct the bug by passing the correct base pointer, `p2p_pgmap`, to
devm_kfree().

Signed-off-by: Sungho Kim <sungho.kim@furiosa.ai>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Logan Gunthorpe <logang@deltatee.com>
Link: https://patch.msgid.link/20250820105714.2939896-1-sungho.kim@furiosa.ai