drm: rename u32 in __u32 in uapi

drm: rename u32 in __u32 in uapi

All other fields use __

Cc: Ben Widawsky <[email protected]>
Fixes: db1689aa61b ("drm: Create a format/modifier blob")
Signed-off-by: Lionel Landwerlin <[email protected]>
Signed-off-by: Daniel Stone <[email protected]>
Reviewed-by: Chris Wilson <[email protected]>
Reviewed-by: Emil Velikov <[email protected]>
Reviewed-by: Ben Widawsky <[email protected]>
Reviewed-by: Daniel Stone <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]