via sysfs even if debugging disabled.  When a firmware error is
captured, it will be dumped to the kernel log (if debug enabled) and
captured in memory to be retrieved via sysfs.

If an error has already been captured, subsequent errors will be
dropped.

The existing error can be cleared by writing to the error log entry.
Signed-off-by: James Ketrenos <jketreno@linux.intel.com>