EDAC/altera: Set DDR and SDMMC interrupt mask before registration

Mask DDR and SDMMC in probe function to avoid spurious interrupts before
registration.  Removed invalid register write to system manager.

Fixes: 1166fde9 ("EDAC, altera: Add Arria10 ECC memory init functions")
Signed-off-by: Niravkumar L Rabara <niravkumar.l.rabara@altera.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/20250425142640.33125-3-matthew.gerlach@altera.com