Reducing the size of ucode_prefix to 25 in the amdgpu_vcn_early_init
function. This would ensure that the total number of characters being
written into fw_name does not exceed its size of 40.

Fixes the below with gcc W=1:
drivers/gpu/drm/amd/amdgpu/amdgpu_vcn.c: In function ‘amdgpu_vcn_early_init’:
drivers/gpu/drm/amd/amdgpu/amdgpu_vcn.c:102:66: warning: ‘snprintf’ output may be truncated before the last format character [-Wformat-truncation=]
  102 |                 snprintf(fw_name, sizeof(fw_name), "amdgpu/%s.bin", ucode_prefix);
      |                                                                  ^
drivers/gpu/drm/amd/amdgpu/amdgpu_vcn.c:102:17: note: ‘snprintf’ output between 12 and 41 bytes into a destination of size 40
  102 |                 snprintf(fw_name, sizeof(fw_name), "amdgpu/%s.bin", ucode_prefix);
      |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/gpu/drm/amd/amdgpu/amdgpu_vcn.c:102:66: warning: ‘snprintf’ output may be truncated before the last format character [-Wformat-truncation=]
  102 |                 snprintf(fw_name, sizeof(fw_name), "amdgpu/%s.bin", ucode_prefix);
      |                                                                  ^
drivers/gpu/drm/amd/amdgpu/amdgpu_vcn.c:102:17: note: ‘snprintf’ output between 12 and 41 bytes into a destination of size 40
  102 |                 snprintf(fw_name, sizeof(fw_name), "amdgpu/%s.bin", ucode_prefix);
      |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/gpu/drm/amd/amdgpu/amdgpu_vcn.c:105:73: warning: ‘.bin’ directive output may be truncated writing 4 bytes into a region of size between 2 and 31 [-Wformat-truncation=]
  105 |                         snprintf(fw_name, sizeof(fw_name), "amdgpu/%s_%d.bin", ucode_prefix, i);
      |                                                                         ^~~~
drivers/gpu/drm/amd/amdgpu/amdgpu_vcn.c:105:25: note: ‘snprintf’ output between 14 and 43 bytes into a destination of size 40
  105 |                         snprintf(fw_name, sizeof(fw_name), "amdgpu/%s_%d.bin", ucode_prefix, i);
      |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Christian König <christian.koenig@amd.com>
Suggested-by: Lijo Lazar <lijo.lazar@amd.com>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>