firewire: ohci: optimize TSB41BA3D detection

Takes less source code and machine code, and less runtime with PHYs
other than TSB41BA3D (e.g. TSB81BA3 with device ID 0x831304 which takes
one instead of six read_paged_phy_reg now).

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>