[POWERPC] UPIO_TSI cleanup

(le32_to_cpu(x) >> 8) & 0xff is a very odd way to spell (x >> 16) & 0xff,
even if that code is hit only on ppc.  The value is host-endian - we've
got it from readl(), after all...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Paul Mackerras <paulus@samba.org>