ATAng - delay probing for non-existent drive

[Bryan Liesner]

The last change to ata-lowlevel (rev 1.11) causes a 10-15 second delay
probing for a drive that's not there:

atapci0: <Promise PDC20269 UDMA133 controller> port 0xa000-0xa00f,0xa400-0xa403,
0xa800-0xa807,0xb000-0xb003,0xb400-0xb407 mem 0xed000000-0xed003fff irq 5 at device 15.0 on pci0
atapci0: [MPSAFE]
ata2: at 0xb400 on atapci0
ata2: [MPSAFE]

  hangs here for about 15 seconds

ata3: at 0xa800 on atapci0
ata3: [MPSAFE]

I have a single drive on ata2.  Reverting back to 1.10 stops the delay.

-Bryan