ACPI: simplify scan.c coding

No functional changes; just remove leftover, unused "buffer" and simplify
control flow (no need to remember error values and goto the end, when we can
simply return the value directly).

Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Len Brown <len.brown@intel.com>