drm/amdgpu/discovery: Add braces to case statements in amdgpu_discovery_table_check()

drm/amdgpu/discovery: Add braces to case statements in amdgpu_discovery_table_check()

When building with a version of clang that supports the narrower
'-fms-anonymous-structs' (as opposed to the wider '-fms-extensions')
along with the associated kernel support (such as in next-20260312 [1]),
there are warnings (or errors with CONFIG_WERROR=y / W=e) from the
switch statement added by commit 47ab777c16c7 ("drm/amdgpu/discovery:
use common function to check discovery table").

  drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c:560:3: error: label followed by a declaration is a C23 extension [-Werror,-Wc23-extensions]
    560 |                 struct ip_discovery_header *ihdr =
        |                 ^
  drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c:568:3: error: label followed by a declaration is a C23 extension [-Werror,-Wc23-extensions]
    568 |                 struct gpu_info_header *ghdr =
        |                 ^
  drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c:576:3: error: label followed by a declaration is a C23 extension [-Werror,-Wc23-extensions]
    576 |                 struct harvest_info_header *hhdr =
        |                 ^
  drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c:584:3: error: label followed by a declaration is a C23 extension [-Werror,-Wc23-extensions]
    584 |                 struct vcn_info_header *vhdr =
        |                 ^
  drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c:592:3: error: label followed by a declaration is a C23 extension [-Werror,-Wc23-extensions]
    592 |                 struct mall_info_header *mhdr =
        |                 ^

If '-fms-extensions' were not present, this would be a hard error in
older clang versions.

Add braces to the case statements that declare variables to clear up the
warnings.

Fixes: 47ab777c16c7 ("drm/amdgpu/discovery: use common function to check discovery table")
Link: https://git.kernel.org/next/linux-next/c/0d3fccf68d9873a3c824fb70be0dbb2c4642aa90
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>