drm: proc: Use minor->index to label things, not PDE->name

Use minor->index to label things, not the name field from the proc_dir_entry
of the /proc/dwm/<minor>/ directory.

Also, use "%u" not "%d" to render the value and use a 12-byte buffer in which
to render the integer, not a 16-byte buffer.  The longest string an unsigned
int can give you is 10 chars (4294967295) plus a NUL, so round up to 12 as the
stack is likely to be 4- or 8-byte aligned.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: dri-devel@lists.freedesktop.org
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>