app/testpmd: fix type of FEC mode parsing output

app/testpmd: fix type of FEC mode parsing output

Passing an uint32_t pointer to an enum pointer parameter causes
pointer-sign warning on Windows (converts between pointers to
integer types with different sign), since enum is implicitly
converted to int on Windows.

And the current enum pointer parameter of that function is actually
misleading and should be fixed as an uint32_t pointer parameter.

Fixes: b19da32e3151 ("app/testpmd: add FEC command")
Cc: stable@dpdk.org
Signed-off-by: Jie Zhou <jizh@linux.microsoft.com>
Reviewed-by: Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>