fm10k: fix possible null pointer deref after kcalloc

When writing a new default redirection table, we needed to populate
a new RSS table using ethtool_rxfh_indir_default. We populated this
table into a region of memory allocated using kcalloc, but never checked
this for NULL. Fix this by moving the default table generation into
fm10k_write_reta. If this function is passed a table, use it. Otherwise,
generate the default table using ethtool_rxfh_indir_default, 4 at at
time.

Fixes: 0ea7fae4 ("fm10k: use ethtool_rxfh_indir_default for default redirection table")
Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>