net: ethernet: nixge: fix NULL dereference

In the Linux kernel, the following vulnerability has been resolved: net: ethernet: nixge: fix NULL dereference In function nixge_hw_dma_bd_release() dereference of NULL pointer priv->rx_bd_v is possible for the case of its allocation failure in nixge_hw_dma_bd_init(). Move for() loop with priv->rx_bd_v dereference under the check for its validity. Found by Linux Verification Center (linuxtesting.org) with SVACE.