drm/debugfs: use octal permissions instead of symbolic permissions

drm/debugfs: use octal permissions instead of symbolic permissions

Currently, debugfs functions are using symbolic macros as permission
bits, but checkpatch reinforces permission bits in the octal form, as
they are more readable and easier to understand [1]. Moreover, using
the symbolic macro S_IFREG is redundant.

Therefore, use octal permission bits in all debugfs functions.

[1] https://docs.kernel.org/dev-tools/checkpatch.html#permissions

Suggested-by: Jani Nikula <jani.nikula@linux.intel.com>
Signed-off-by: Maíra Canal <mcanal@igalia.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Maíra Canal <mairacanal@riseup.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20230105193039.287677-1-mcanal@igalia.com