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