ixgbe: fix SFF data dumps of SFP+ modules

This patch fixes several issues with the previous implementation of the
SFF data dump of SFP+ modules:

- removed the __IXGBE_READ_I2C flag - I2C access locking is handled in the
  HW specific routines

- fixed the read loop to read data from ee->offset to ee->len

- the reads fail if __IXGBE_IN_SFP_INIT is set in the process - this is
  needed because on some HW I2C operations can take long time and disrupt
  the SFP and link detection process

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