EDAC/altera: Do less intrusive error injection

Improve the Arria10 and Stratix10 error injection routine
by reading the data and changing just 1 bit before writing
back out. Previous routine would overwrite the first bytes
to 0 then change 1 bit but this method is less intrusive.

Signed-off-by: Thor Thayer <thor.thayer@linux.intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: James Morse <james.morse@arm.com>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Cc: linux-edac <linux-edac@vger.kernel.org>
Link: https://lkml.kernel.org/r/1553635771-32693-1-git-send-email-thor.thayer@linux.intel.com
diff --git a/drivers/edac/altera_edac.h b/drivers/edac/altera_edac.h
index 60513f2..1532ec9 100644
--- a/drivers/edac/altera_edac.h
+++ b/drivers/edac/altera_edac.h
@@ -321,7 +321,7 @@ struct altr_sdram_mc_data {
 #define ECC_BLK_STARTACC_OFST             0x7C
 
 #define ECC_XACT_KICK                     0x10000
-#define ECC_WORD_WRITE                    0xF
+#define ECC_WORD_WRITE                    0xFF
 #define ECC_WRITE_DOVR                    0x101
 #define ECC_WRITE_EDOVR                   0x103
 #define ECC_READ_EOVR                     0x2