powerpc/pci: Fix return type of BUID_{HI,LO} macros

BUID_HI and BUID_LO are used to pass data to call_rtas, which expects
ints or u32s. But the macro doesn't cast the return, so the result is
still u64. Use the upper_32_bits and lower_32_bits macros that have been
added to kernel.h.

Found by getting printf format errors trying to debug print the args, no
actual code change for 64 bit kernels where the macros are actually
used.

Signed-off-by: Milton Miller <miltonm@bga.com>
Signed-off-by: Nishanth Aravamudan <nacc@us.ibm.com>
Acked-by: Linas Vepstas <linasvepstas@gmail.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>