wifi: b43: remove empty switch statement

There's a TODO here, just move the dependency on phy->rev
into the comment. Not that this driver is likely to get
any updates.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20220904212910.ea00a892e41b.I709217fc307125f8670c7f6a9093111b46194131@changeid