docs: marvell: update path in marvell documentation

Change-Id: I0cebbaa900aa518700f13cbf02f8a97e0c76b21c
Signed-off-by: Grzegorz Jaszczyk <jaz@semihalf.com>

docs/plat/marvell/armada/porting.rst

@@ -36,7 +36,7 @@ memory map is required.
 .. note::
    For a detailed information on how CCU, IOWIN, AXI-MBUS & IOB work, please
    refer to the SoC functional spec, and under
-   ``docs/marvell/misc/mvebu-[ccu/iob/amb/io-win].txt`` files.
+   ``docs/plat/marvell/armada/misc/mvebu-[ccu/iob/amb/io-win].rst`` files.
 
 boot loader recovery (marvell_plat_config.c)
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~