dma-buf: make kobj_type structure constant

Since commit ee6d3dd4ed48 ("driver core: make kobj_type constant.")
the driver core allows the usage of const struct kobj_type.

Take advantage of this to constify the structure definition to prevent
modification at runtime.

Signed-off-by: Thomas Weißschuh <[e-mail]>
Reviewed-by: Christian König <[e-mail]>
Signed-off-by: Christian König <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/dma-buf/dma-buf-sysfs-stats.c

···
 	kfree(sysfs_entry);
 }
 
-static struct kobj_type dma_buf_ktype = {
+static const struct kobj_type dma_buf_ktype = {
 	.sysfs_ops = &dma_buf_stats_sysfs_ops,
 	.release = dma_buf_sysfs_release,
 	.default_groups = dma_buf_stats_default_groups,