ixgbe: fix SFF data dumps of SFP+ modules from an offset

This patch fixes the read loop for the I2C data to account for the offset.

Also includes a whitespace cleanup and removes ret_val as it is not needed.

CC: Ben Hutchings <bhutchings@solarflare.com>
Reported-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: Emil Tantilov <emil.s.tantilov@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Reviewed-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>