nfcsim.c: Fix error checking for debugfs_create_dir

This patch fixes the error checking in nfcsim.c.
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>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: David S. Miller <davem@davemloft.net>