doc: update Marvell driver link
doc: update Marvell driver link

Change the incorrect driver documentation link to fix
following documentation build warning.

$ make doc-guides-html
sphinx processing guides-html...
doc/guides/rel_notes/release_17_11.rst:58:
WARNING: unknown document: ../nics/mrvl

Fixes: fe93968722af ("net/mrvl: rename PMD as mvpp2")

Signed-off-by: Jerin Jacob <5bca7d2a432bc0f5422b70b2701a4e4fa32edd00@caviumnetworks.com>
Acked-by: Marko Kovacevic <32a723043e16bf2a3185e32c2e613ae1ee55288f@intel.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk