i2c: Improve formatting of i2c dump function

If an i2c message is for just one byte, instead of logging it with a
hexdump after logging the other message info, just added the one byte to
the same log message.

Since most i2c messages are one byte, this significantly reduces the
number of messages and lines needed to log i2c transactions, from three
line per message to just one.  It's also a lot easier to read.

Signed-off-by: Trent Piepho <trent.piepho@igorinstitute.com>