ixgbe: clear the data field in ixgbe_read_i2c_byte_generic

Clear the data field in ixgbe_read_i2c_byte_generic so it does not
accumulate 1 bit using the same variable multiple times.

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