pci: fix bsd build with gcc

pci: fix bsd build with gcc

GCC 4.8 raises this error:
lib/librte_eal/bsdapp/eal/eal_pci.c:453:15: error: cast discards
'__attribute__((const))' qualifier from pointer target type
   .pi_data = *(u_int32_t *)buf,
               ^

Note: this assignment seems useless because pi_data is filled
with memset later.

Fixes: 632b2d1deeed ("eal: provide functions to access PCI config")

Signed-off-by: Thomas Monjalon <thomas.monjalon@6wind.com>
Acked-by: Bruce Richardson <bruce.richardson@intel.com>