xen/gntdev: gntdev.h: drop a duplicated word

Drop the repeated word "of" in a comment.
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Reviewed-by: Juergen Gross <jgross@suse.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: xen-devel@lists.xenproject.org
Link: https://lore.kernel.org/r/20200719003317.21454-1-rdunlap@infradead.orgSigned-off-by: Juergen Gross <jgross@suse.com>

include/uapi/xen/gntdev.h

@@ -66,7 +66,7 @@ struct ioctl_gntdev_map_grant_ref {
 
 /*
  * Removes the grant references from the mapping table of an instance of
- * of gntdev. N.B. munmap() must be called on the relevant virtual address(es)
+ * gntdev. N.B. munmap() must be called on the relevant virtual address(es)
  * before this ioctl is called, or an error will result.
  */
 #define IOCTL_GNTDEV_UNMAP_GRANT_REF \