Blackfin: Annotate clear_user 'to' parameter with __user

The 'to' parameter of clear_user is supposed to take a userspace pointer, so
annotate it with __user. This fixes the following and similar sparse warnings:

	fs/binfmt_elf_fdpic.c:714:35: warning: incorrect type in argument 1 (different address spaces)
	fs/binfmt_elf_fdpic.c:714:35:    expected void [noderef] <asn:1>*to
	fs/binfmt_elf_fdpic.c:714:35:    got void *<noident>
	fs/binfmt_elf_fdpic.c:1119:29: warning: incorrect type in argument 1 (different address spaces)
	fs/binfmt_elf_fdpic.c:1119:29:    expected void *to
	fs/binfmt_elf_fdpic.c:1119:29:    got void [noderef] <asn:1>*<noident>

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Bob Liu <lliubbo@gmail.com>