flashchips: Mark S25FL208K as tested

As report by Frédéric Germain on 2017-12-17.

Change-Id: I0a7fc10e75f4a675de41e9765525defe2d2640e4
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/28883
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
diff --git a/flashchips.c b/flashchips.c
index e517a49..d2773d6 100644
--- a/flashchips.c
+++ b/flashchips.c
@@ -12215,7 +12215,7 @@
 		.total_size	= 1024,
 		.page_size	= 256,
 		.feature_bits	= FEATURE_WRSR_WREN,
-		.tested		= TEST_UNTESTED,
+		.tested		= TEST_OK_PREW,
 		.probe		= probe_spi_rdid,
 		.probe_timing	= TIMING_ZERO,
 		.block_erasers	= {