net: mvpp2: debugfs: Add pmap to fs dump

There was an unused variable 'mvpp2_dbgfs_prs_pmap_fops'
Added a usage consistent with other fops to dump pmap
to userspace.

Cc: clang-built-linux@googlegroups.com
Link: https://github.com/ClangBuiltLinux/linux/issues/529
Signed-off-by: Nathan Huckleberry <nhuck@google.com>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>