image: fit: Fix parameter name for hash algorithm

Fix inconsistent function parameter name of the hash algorithm.

Signed-off-by: Chia-Wei Wang <chiawei_wang@aspeedtech.com>
Fixes: 92055e13 ("image: Drop if/elseif hash selection in calculate_hash()")
Reviewed-by: Joel Stanley <joel@jms.id.au>
Reviewed-by: Simon Glass <sjg@chromium.org>