fwts: build failure on fadt tests with gcc 4.6 (trusty)

[Colin Ian King]

const fwts_acpi_gas null_gas = { 0 } causes a build failure with older compilers, such as gcc 4.6 (on Trusty):

acpi/fadt/fadt.c: In function 'acpi_table_check_fadt_reduced_hardware':
acpi/fadt/fadt.c:447:2: error: missing initializer [-Werror=missing-field-initializers]
acpi/fadt/fadt.c:447:2: error: (near initialization for 'null_gas.register_bit_width') [-Werror=missing-field-initializers]

make null_gas a static const - this will then be initialized as all zeros just once at run time and it's compatible with older versions of gcc too. Note this is a read-only struct, so this is fine to init like this

[Colin Ian King (colin-king)]

Fix send to fwts-devel for review: https://lists.ubuntu.com/archives/fwts-devel/2016-February/007591.html

[Colin Ian King (colin-king)]

This fixes build errors: https://launchpadlibrarian.net/242454993/buildlog_ubuntu-precise-armhf.fwts_16.01.00-0ubuntu1+201602241046~ubuntu12.04.1_BUILDING.txt.gz