wifi: rtl818x: Fix potential memory leaks in rtl8180_init_rx_ring()

wifi: rtl818x: Fix potential memory leaks in rtl8180_init_rx_ring()

In rtl8180_init_rx_ring(), memory is allocated for skb packets and DMA
allocations in a loop. When an allocation fails, the previously
successful allocations are not freed on exit.

Fix that by jumping to err_free_rings label on error, which calls
rtl8180_free_rx_ring() to free the allocations. Remove the free of
rx_ring in rtl8180_init_rx_ring() error path, and set the freed
priv->rx_buf entry to null, to avoid double free.

Fixes: f653211197f3 ("Add rtl8180 wireless driver")
Signed-off-by: Abdun Nihaal <nihaal@cse.iitm.ac.in>
Reviewed-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Link: https://patch.msgid.link/20251114094527.79842-1-nihaal@cse.iitm.ac.in