ACPI / PCI: pci_slot: Use more common logging style

Use generic pr_<level> functions with pr_fmt for info and err.

This also reduces object size a trivial bit:

$ size drivers/acpi/pci_slot.o*
   text	   data	    bss	    dec	    hex	filename
    935	    752	      5	   1692	    69c	drivers/acpi/pci_slot.o.new
   1027	    752	      5	   1784	    6f8	drivers/acpi/pci_slot.o.old

Miscellanea:

o Remove unnecessary OOM message as k.alloc functions get a generic
  stack dump on OOM
o Remove unnecessary embedded prefix from a dbg() message

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>