spi: ch341: fix out-of-bounds memory access in ch341_transfer_one

In the Linux kernel, the following vulnerability has been resolved: spi: ch341: fix out-of-bounds memory access in ch341_transfer_one Discovered by Atuin - Automated Vulnerability Discovery Engine. The 'len' variable is calculated as 'min(32, trans->len + 1)', which includes the 1-byte command header. When copying data from 'trans->tx_buf' to 'ch341->tx_buf + 1', using 'len' as the length is incorrect because: 1. It causes an out-of-bounds read from 'trans->tx_buf' (which has size 'trans->len', i.e., 'len - 1' in this context). 2. It can cause an out-of-bounds write to 'ch341->tx_buf' if 'len' is CH341_PACKET_LENGTH (32). Writing 32 bytes to ch341->tx_buf + 1 overflows the buffer. Fix this by copying 'len - 1' bytes.