checkpatch: Fix use of uninitialized value

checkpatch: Fix use of uninitialized value

checkfilename() doesn't always set $acpi_testexpected. Fix the following
warning:

Use of uninitialized value $acpi_testexpected in string eq at
 ./scripts/checkpatch.pl line 1529.

Fixes: d2f1af0e4120 ("checkpatch: don't emit warning on newly created acpi data files")
Cc: isaku.yamahata@intel.com
Signed-off-by: Greg Kurz <groug@kaod.org>
Message-Id: <161786467973.295167.5612704777283969903.stgit@bahia.lan>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>