igc: Fix a bogus register write in igc_if_queues_free()

[markj]

Summary

As explained in PR 277038, iflib calls IFDI_DETACH() and then
IFDI_QUEUES_FREE(). With igc, the latter writes to a register after it
has been unmapped.

igc_if_detach() already calls igc_release_hw_control(), and looking at
callers of igc_if_queues_free(), that appears to be sufficient. So,
just remove the igc_release_hw_control() call.

PR: 277038
Diagnosed by: Mike Belanger <[e-mail]>

Test Plan

I have no igc hardware and can't test this, any testing would be appreciated.

[kbowling]

This change looks logically correct to me and matches e1000.

I have tested on an I225-IT(2) using devctl and see no issues with attach/detach.