hexagon: Use raw_copy_to_user

Commit ac4691fa ("hexagon: switch to RAW_COPY_USER") replaced
__copy_to_user_hexagon() with raw_copy_to_user(), but did not catch
all callers, resulting in the following build error.

arch/hexagon/mm/uaccess.c: In function '__clear_user_hexagon':
arch/hexagon/mm/uaccess.c:40:3: error:
	implicit declaration of function '__copy_to_user_hexagon'

Fixes: ac4691fa

 ("hexagon: switch to RAW_COPY_USER")
Cc: Al Viro <viro@zeniv.linux.org.uk>
Acked-by: Al Viro <viro@zeniv.linux.org.uk>
Acked-by: Richard Kuo <rkuo@codeaurora.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>