drm/amdgpu: silence UBSAN warning

Convert a variable sized array from [1] to [].
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -3583,7 +3583,7 @@ struct atom_gpio_voltage_object_v4
    uint8_t  phase_delay_us;                      // phase delay in unit of micro second
    uint8_t  reserved;   
    uint32_t gpio_mask_val;                         // GPIO Mask value
-   struct atom_voltage_gpio_map_lut voltage_gpio_lut[1];
+   struct atom_voltage_gpio_map_lut voltage_gpio_lut[] __counted_by(gpio_entry_num);
 };
 
 struct  atom_svid2_voltage_object_v4