drm/amdkfd: fix uninitialized variable use

When CONFIG_ACPI is disabled, we never initialize the acpi_table
structure in kfd_create_crat_image_virtual:

drivers/gpu/drm/amd/amdkfd/kfd_crat.c: In function 'kfd_create_crat_image_virtual':
drivers/gpu/drm/amd/amdkfd/kfd_crat.c:888:40: error: 'acpi_table' may be used uninitialized in this function [-Werror=maybe-uninitialized]

The undefined behavior also happens for any other acpi_get_table()
failure, but then the compiler can't warn about it.

This adds an error check that prevents the structure from
being used in error, avoiding both the undefined behavior and
the warning about it.

Fixes: 520b8fb7 ("drm/amdkfd: Add topology support for CPUs")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Oded Gabbay <oded.gabbay@gmail.com>