net: dsa: sja1105: Fix memory leak on meta state machine error path

When RX timestamping is enabled and two link-local (non-meta) frames are
received in a row, this constitutes an error.

The tagger is always caching the last link-local frame, in an attempt to
merge it with the meta follow-up frame when that arrives. To recover
from the above error condition, the initial cached link-local frame is
dropped and the second frame in a row is cached (in expectance of the
second meta frame).

However, when dropping the initial link-local frame, its backing memory
was being leaked.

Fixes: f3097be2 ("net: dsa: sja1105: Add a state machine for RX timestamping")
Signed-off-by: Vladimir Oltean <olteanv@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>