e1000e: Minor flow correction in e1000_shutdown function

Add curly braces to avoid entering to an if statement where it is not
always required in e1000_shutdown function.
This improves code readability and might prevent non-deterministic
behaviour in the future.

Signed-off-by: Vitaly Lifshits <vitaly.lifshits@intel.com>
Tested-by: Naama Meir <naamax.meir@linux.intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
Link: https://lore.kernel.org/r/20240301184806.2634508-5-anthony.l.nguyen@intel.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>