nfc: pn533: allocate rx skb before consuming bytes

In the Linux kernel, the following vulnerability has been resolved:

nfc: pn533: allocate rx skb before consuming bytes

pn532_receive_buf() reports the number of accepted bytes to the serdev

core. The current code consumes bytes into recv_skb and may already hand

a complete frame to pn533_recv_frame() before allocating a fresh receive

buffer.

If that alloc_skb() fails, the callback returns 0 even though it has

already consumed bytes, and it leaves recv_skb as NULL for the next

receive callback. That breaks the receive_buf() accounting contract and

can also lead to a NULL dereference on the next skb_put_u8().

Allocate the receive skb lazily before consuming the next byte instead.

If allocation fails, return the number of bytes already accepted.