lib: error-inject: remove error checking for debugfs_create_dir()

It is expected that most callers should _ignore_ the errors return by
debugfs_create_dir() in ei_debugfs_init().

Link: https://lkml.kernel.org/r/20230719144355.6720-1-machel@vivo.com


Signed-off-by: Wang Ming <machel@vivo.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>