ixgbe: remove return code for functions that always return 0

Since ixgbe_raise_i2c_clk() can never return anything else than 0
this patch removes it's return value and all checks for it.

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>