firewire: ohci: dump_stack() for PHY regs read/write failures

A stack trace is an invaluable tool in determining the basis
and cause of PHY regs read/write failures.

Include PHY reg addr (and value for writes) in the diagnostic.

[Stefan R:  changed whitespace]

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>