i2c: fix parameter of trace_i2c_result

According to the event i2c_result defined in include/trace/events/i2c.h,
the second parameter should be the number of messages instead of the
ended loop index. The value of ended loop index is the same as ret.

Signed-off-by: Ahbong Chang <cwahbong@google.com>
Reviewed-by: Todd Poynor <toddpoynor@google.com>
Reviewed-by: David Howells <dhowells@redhat.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>