spi-dw-core.c: Fix error checking for debugfs_create_dir

This patch fixes the error checking in spi-dw-core.c in
debugfs_create_dir. The DebugFS kernel API is developed in
a way that the caller can safely ignore the errors that
occur during the creation of DebugFS nodes.

Signed-off-by: Osama Muhammad <osmtendev@gmail.com>
Link: https://lore.kernel.org/r/20230520224025.14928-1-osmtendev@gmail.com


Signed-off-by: Mark Brown <broonie@kernel.org>