Documentation: arm: Fix marvell file name

Fixes: dc7a12b ("docs: arm: convert docs to ReST and rename to *.rst")
Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/20210121193418.22678-1-pali@kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Author: pali

Documentation/arm/index.rst

@@ -33,7 +33,7 @@ SoC-specific documents
 
    ixp4xx
 
-   marvel
+   marvell
    microchip
 
    netwinder