net/mlx: fix debug build with gcc 6.1

net/mlx: fix debug build with gcc 6.1

With recent gcc versions, e.g. gcc 6.1, compilation of mlx drivers with
debug enabled produces lots of errors complaining that "pedantic" is
not a warning level that can be ignored.

error: ‘-pedantic’ is not an option that controls warnings [-Werror=pragmas]
 #pragma GCC diagnostic ignored "-pedantic"
                                 ^~~~~~~~~~~

These errors can be removed by changing the "-pedantic" to "-Wpedantic".

Fixes: 7fae69eeff13 ("mlx4: new poll mode driver")
Fixes: 771fa900b73a ("mlx5: introduce new driver for Mellanox ConnectX-4 adapters")
Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
Acked-by: Adrien Mazarguil <adrien.mazarguil@6wind.com>