staging: axis-fifo: flush RX FIFO on read errors

Flush stale data from the RX FIFO in case of errors, to avoid reading
old data when new packets arrive.

Commit c6e8d85f ("staging: axis-fifo: Remove hardware resets for
user errors") removed full FIFO resets from the read error paths, which
fixed potential TX data losses, but introduced this RX issue.

Fixes: c6e8d85f ("staging: axis-fifo: Remove hardware resets for user errors")
Cc: stable@vger.kernel.org
Signed-off-by: Ovidiu Panait <ovidiu.panait.oss@gmail.com>
Link: https://lore.kernel.org/r/20250912101322.1282507-2-ovidiu.panait.oss@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>