UBI: always dump flash contents in case of errors

UBI (and UBIFS) are a bit over-engineered WRT debugging. The idea was to
link as few as possible when debugging is disabled, but the downside is
that most people produce bug reports which are difficult to understand.

Always dump the flash contents in case of errors, not only when debugging is
enabled.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@linux.intel.com>