thunderbolt: debugfs: Don't stop reading SB registers if just one fails

thunderbolt: debugfs: Don't stop reading SB registers if just one fails

The GEN4 TxFFE register is not part of the USB4 v1.0 specification, so
understandably some pre-USB4v2 retimers (like the Parade PS8830) don't
seem to implement it.

The immediate idea to counter this would be to introduce a version
check for that specific register, but on a second thought, the current
flow only returns a quiet -EIO if there's any failures, without hinting
at what the actual problem is.

To take care of both of these issues, simply print an error line for
each SB register read that fails and go on with attempting to read the
others.

Note that this is not quite in-spec behavior ("The SB Register Space
registers shall have the structure and fields described in Table 4-17.
Registers not listed in Table 4-20 are undefined and shall not be
used."), but it's the easiest fix that shouldn't have real-world bad
side effects.

Fixes: 6d241fa00159 ("thunderbolt: Add sideband register access to debugfs")
Signed-off-by: Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>