spi: img-spfi: Implement a handle_err() callback

The driver can be greatly simplified by moving the transfer timeout
handling to a handle_err() callback.

Signed-off-by: Ezequiel Garcia <ezequiel.garcia@imgtec.com>
Signed-off-by: Andrew Bresticker <abrestic@chromium.org>
Signed-off-by: Mark Brown <broonie@kernel.org>