pata_legacy: correctly mask recovery field for HT6560B

According to the HT6560H datasheet, the recovery timing field is 4-bit wide,
with a value of 0 meaning 16 cycles. Correct obvious thinko in the recovery
field mask.

Signed-off-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Cc: stable@kernel.org
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>