e1000e: use ktime_get_real_ns() in e1000e_systim_reset()

e1000e: use ktime_get_real_ns() in e1000e_systim_reset()

Replace ktime_to_ns(ktime_get_real()) with the direct equivalent
ktime_get_real_ns() in e1000e_systim_reset().  Using the combined helper
avoids the unnecessary intermediate ktime_t variable and makes the
intent clearer.

Suggested-by: Jacob Keller <jacob.e.keller@intel.com>
Suggested-by: Simon Horman <horms@kernel.org>
Signed-off-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
Tested-by: Avigail Dahan <avigailx.dahan@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
Link: https://patch.msgid.link/20260609213559.178657-9-anthony.l.nguyen@intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>