docs: PCI: pci.rst: avoid using ReST :doc:`foo` markup

The :doc:`foo` tag is auto-generated via automarkup.py.
So, use the filename at the sources, instead of :doc:`foo`.
Signed-off-by: NMauro Carvalho Chehab <mchehab+huawei@kernel.org>
Acked-by: NBjorn Helgaas <bhelgaas@google.com>
Link: https://lore.kernel.org/r/8697cf945390f6b45fefb4c5fe22ed1c8070e32e.1623824363.git.mchehab+huawei@kernel.orgSigned-off-by: NJonathan Corbet <corbet@lwn.net>

Documentation/PCI/pci.rst

@@ -265,7 +265,7 @@ Set the DMA mask size
 ---------------------
 .. note::
    If anything below doesn't make sense, please refer to
-   :doc:`/core-api/dma-api`. This section is just a reminder that
+   Documentation/core-api/dma-api.rst. This section is just a reminder that
    drivers need to indicate DMA capabilities of the device and is not
    an authoritative source for DMA interfaces.
 
@@ -291,7 +291,7 @@ Many 64-bit "PCI" devices (before PCI-X) and some PCI-X devices are
 Setup shared control data
 -------------------------
 Once the DMA masks are set, the driver can allocate "consistent" (a.k.a. shared)
-memory.  See :doc:`/core-api/dma-api` for a full description of
+memory.  See Documentation/core-api/dma-api.rst for a full description of
 the DMA APIs. This section is just a reminder that it needs to be done
 before enabling DMA on the device.
 
@@ -421,7 +421,7 @@ owners if there is one.
 
 Then clean up "consistent" buffers which contain the control data.
 
-See :doc:`/core-api/dma-api` for details on unmapping interfaces.
+See Documentation/core-api/dma-api.rst for details on unmapping interfaces.
 
 
 Unregister from other subsystems