flashchips: Mark Macronix MX25U12835F as tested

As reported by David Martinka on the mailing list.

Erase has not been tested, but since writes are reported as working, it
is very likely erase works as well.

Change-Id: I172453fe902ccface2a3a85817d775d45dd7cf80
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/28812
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>
diff --git a/flashchips.c b/flashchips.c
index aa5d9bf..e5f78aa 100644
--- a/flashchips.c
+++ b/flashchips.c
@@ -8572,7 +8572,7 @@
 		.page_size	= 256,
 		/* OTP: 512B total; enter 0xB1, exit 0xC1 */
 		.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	=