RDMA/cxgb4: Fix dereg_skb leak and double free in write_tpt_entry()

In the Linux kernel, the following vulnerability has been resolved: RDMA/cxgb4: Fix dereg_skb leak and double free in write_tpt_entry() When the device is in the fatal error state, write_tpt_entry() returns -EIO before handing the caller's preallocated skb to the transmit path; its allocation-failure returns do the same. c4iw_dereg_mr() ignores the error and frees mhp, leaking mhp->dereg_skb. c4iw_get_dma_mr() instead frees the skb a second time after dereg_mem() already consumed it, a double free. Make write_tpt_entry() the sole owner of a non-NULL skb, freeing it on every return preceding handoff to c4iw_ofld_send(): fatal error, tpt and stag allocation failure. c4iw_ofld_send() consumes the skb on success and error alike, so drop the redundant kfree_skb() in c4iw_get_dma_mr() after dereg_mem().