net/sfc/base: fix signed/unsigned mismatch

net/sfc/base: fix signed/unsigned mismatch

Use UINT32_MAX instead of assigning -1 to a uint32_t variable to
resolve "conversion from 'int' to 'uint32_t', signed/unsigned mismatch"
errors produced by the Visual Studio 2017 toolchain [with the default
/W4 /WX C compiler options which set warning level 4 and treat warnings
as errors].

Fixes: 107cf1d792cb ("net/sfc/base: move limits config to ef10 NIC board config")
Cc: stable@dpdk.org
Signed-off-by: Andrew Lee <alee@solarflare.com>
Signed-off-by: Andrew Rybchenko <arybchenko@solarflare.com>