hwmon: (pmbus/adm1266) include PEC byte in pmbus_block_xfer read buffer

adm1266_pmbus_block_xfer() sets up the read transaction with

	.buf = data->read_buf,
	.len = ADM1266_PMBUS_BLOCK_MAX + 2,

but read_buf in struct adm1266_data is declared as

	u8 read_buf[ADM1266_PMBUS_BLOCK_MAX + 1];

For a max-length block response (length byte = 255 + up to 1 PEC
byte), the i2c controller is told to write 257 bytes into a 256-byte
buffer, putting one byte past the end of read_buf.  The same response
also makes the subsequent PEC compare

	if (crc != msgs[1].buf[msgs[1].buf[0] + 1])

read a byte beyond the array.

Bump the read_buf declaration to ADM1266_PMBUS_BLOCK_MAX + 2 so the
buffer can hold the length byte, up to 255 payload bytes, and the PEC
byte the i2c_msg length already accounts for.

Fixes: 407dc802 ("hwmon: (pmbus/adm1266) Add Block process call")
Cc: stable@vger.kernel.org
Signed-off-by: Abdurrahman Hussain <abdurrahman@nexthop.ai>
Link: https://lore.kernel.org/r/20260515-adm1266-fixes-v1-4-1c1ea1349cfe@nexthop.ai


Signed-off-by: Guenter Roeck <linux@roeck-us.net>