iasl(8) expects integer fields in data tables to be specified as hexadecimal
values. Therefore the bit width of the "PM Timer Block" was actually being
interpreted as 50-bits instead of the expected 32-bit.

This eliminates an error message emitted by a Linux 3.17 guest during boot:
"Invalid length for FADT/PmTimerBlock: 50, using default 32"

Reviewed by: grehan
MFC after: 1 week