raiden_debug_spi: Fix memleak

Change-Id: Ib9d99fefda812d20265db47be353c844f8b77129
Found-by: Coverity Scan #1420204
Signed-off-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-on: https://review.coreboot.org/c/flashrom/+/40969


Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>