ide: ide_get_best_pio_mode() returns incorrect IORDY setting (take 2)

The function ide_get_best_pio_mode() fails to return the correct IORDY setting
for the explicitly specified modes -- fix this along with the heading comment,
and also remove the long commented out code.

Also, while at it, correct the misliading comment about the PIO cycle time in
<linux/ide.h> -- it actually consists of only the active and recovery periods,
with only some chips also including the address setup time into equation...

[ bart: sl82c105 seems to be currently the only driver affected by this fix ]

Signed-off-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>