ixgbe: Clarify the values of the returning status

Converting s32 functions to regular int in the previous patch of the series
caused triggering smatch warnings about missing error code.

New smatch warnings:
drivers/net/ethernet/intel/ixgbe/ixgbe_x550.c:2884 ixgbe_get_lcd_t_x550em() warn: missing error code? 'status'
drivers/net/ethernet/intel/ixgbe/ixgbe_x550.c:3130 ixgbe_enter_lplu_t_x550em() warn: missing error code? 'status'

Old smatch warnings:
drivers/net/ethernet/intel/ixgbe/ixgbe_x550.c:2890 ixgbe_get_lcd_t_x550em() warn: missing error code? 'status'

Fix it by clearly stating returning error code as 0.

Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/r/202401041701.6QKTsZmx-lkp@intel.com/
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Jedrzej Jagielski <jedrzej.jagielski@intel.com>
Tested-by: Pucha Himasekhar Reddy <himasekharx.reddy.pucha@intel.com> (A Contingent worker at Intel)
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>