EDAC/altera: Use correct write width with the INTTEST register

On the SoCFPGA platform, the INTTEST register supports only 16-bit writes.
A 32-bit write triggers an SError to the CPU so do 16-bit accesses only.

  [ bp: AI-massage the commit message. ]

Fixes: c7b4be8d ("EDAC, altera: Add Arria10 OCRAM ECC support")
Signed-off-by: Niravkumar L Rabara <niravkumar.l.rabara@intel.com>
Signed-off-by: Matthew Gerlach <matthew.gerlach@altera.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Acked-by: Dinh Nguyen <dinguyen@kernel.org>
Cc: stable@kernel.org
Link: https://lore.kernel.org/20250527145707.25458-1-matthew.gerlach@altera.com