[PATCH] 8390 Tx fix for non i386 machines

While this is true, E8390_CMD is zero on i386, and thus there should be no
effect for these machines.  Machines like Mac, Amiga etc. which use Alan's
clever register mapping may have a non-zero E8390_CMD and result in bogus
"transmitter busy" type messages from this bug.

Fixes BUG# 3991.