flashchips.c: mark EN25S64 as TESTED_OK_PREW

The chip was marked as TESTED_OK_PREW in the cros tree by
`commit b2f900273aac329b82089e4dbc5a8ba3d032fff0`.

Quoting from the original commit message:
> TEST=read and write BIOS on glimmer with Eon device.

Change-Id: I13dc3e6bde9e4581fdd5856a412918784b913fbc
Signed-off-by: Nikolai Artemiev <nartemiev@google.com>
Original-Reviewed-on: https://review.coreboot.org/c/flashrom/+/51734
Original-Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Original-Reviewed-by: Edward O'Callaghan <quasisec@chromium.org>
Reviewed-on: https://review.coreboot.org/c/flashrom-stable/+/70948
Reviewed-by: Nico Huber <nico.h@gmx.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/flashchips.c b/flashchips.c
index 2e617e3..2555d48 100644
--- a/flashchips.c
+++ b/flashchips.c
@@ -5403,7 +5403,7 @@
 		.page_size	= 256,
 		/* OTP: 512B total; enter 0x3A */
 		.feature_bits	= FEATURE_WRSR_WREN | FEATURE_OTP | FEATURE_QPI,
-		.tested		= TEST_UNTESTED,
+		.tested		= TEST_OK_PREW,
 		.probe		= probe_spi_rdid,
 		.probe_timing	= TIMING_ZERO,
 		.block_erasers	=