iommu: apple-dart: fix potential null pointer deref

iommu: apple-dart: fix potential null pointer deref

If kzalloc() fails, accessing cfg->supports_bypass causes a null pointer dereference.

Fix by checking for NULL immediately after allocation and returning -ENOMEM.

Fixes: 3bc0102835f6 ("iommu: apple-dart: Allow mismatched bypass support")
Signed-off-by: Qasim Ijaz <qasdev00@gmail.com>
Reviewed-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Link: https://lore.kernel.org/r/20250314230102.11008-1-qasdev00@gmail.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>