drm/amdgpu/atomfirmware: silence UBSAN warning

This is a variable sized array.

Link: https://lists.freedesktop.org/archives/amd-gfx/2024-June/110420.html
Tested-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

Author: alexdeucher

drivers/gpu/drm/amd/include/atomfirmware.h

@@ -734,7 +734,7 @@ struct atom_gpio_pin_lut_v2_1
 {
   struct  atom_common_table_header  table_header;
   /*the real number of this included in the structure is calcualted by using the (whole structure size - the header size)/size of atom_gpio_pin_lut  */
-  struct  atom_gpio_pin_assignment  gpio_pin[8];
+  struct  atom_gpio_pin_assignment  gpio_pin[];
 };