do not accept "garbage" from acpi firmware performance data (FPDT)

00000000  46 42 50 54 38 00 00 00  02 00 30 02 00 00 00 00  |FBPT8.....0.....|
00000010  23 45 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |#E..............|
00000020  f5 6a 51 00 00 00 00 00  00 00 00 00 00 00 00 00  |.jQ.............|
00000030  00 00 00 00 00 00 00 00  70 74 61 6c 58 00 00 00  |........ptalX...|