ntb: amd: Drop unnecessary error check for debugfs_create_dir

This patch removes the error checking for debugfs_create_dir in
ntb_hw_amd.c. This is because 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. The debugfs APIs have
a IS_ERR() judge in start_creating() which can handle it
gracefully. so these checks are unnecessary.

Signed-off-by: Ruan Jinjie <ruanjinjie@huawei.com>
Acked-by: Sanjay R Mehta <sanju.mehta@amd.com>
Signed-off-by: Jon Mason <jdmason@kudzu.us>