MIPS: uaccess: Remove get_fs/set_fs call sites

Use new helpers to access user/kernel for functions, which are used with
user/kernel pointers. Instead of dealing with get_fs/set_fs select
user/kernel access via parameter.

Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>