drm: Add missing __user annotation

The drm_copy_field() function copies strings into userspace buffers, so
the first parameter needs to have a __user annotation to avoid warnings
from the sparse checker.

Signed-off-by: Thierry Reding <[e-mail]>
Reviewed-by: David Herrmann <[e-mail]>
Signed-off-by: Dave Airlie <[e-mail]>

drivers/gpu/drm/drm_drv.c

···
 /**
  * Copy and IOCTL return string to user space
  */
-static int drm_copy_field(char *buf, size_t *buf_len, const char *value)
+static int drm_copy_field(char __user *buf, size_t *buf_len, const char *value)
 {
 	int len;