Change memory allocation for acpiphp slots

Change the "struct slot" that acpiphp uses for managing it's slots to
directly contain the memory for the needed struct hotplug_slot_info and
the slot's name. This way we need only two memory allocations per slot
instead of four.

While we are at it: make_slot_name() is just a wrapper around snprintf()
knowing the right arguments to call it. Since the function makes just one
function call and is only called from one place I inlined it by hand.

Finally this fixes a possible bug waiting for someone to hit it. There were
two unused local variables in acpiphp_register_hotplug_slot(). gcc did not
find them because they were used in memory allocations with sizeof(*var).
They had the same types as the target of the allocation, but nevertheless
this was just weird.
Signed-off-by: Rolf Eike Beer <eike-hotplug@sf-tec.de>
Acked-by: Matthew Wilcox <matthew@wil.cx>
Signed-off-by: Kristen Carlson Accardi <kristen.c.accardi@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>