drm/amdgpu: Fix bounds checking in amdgpu_ras_is_supported()

The "block" variable can be set by the user through debugfs, so it can
be quite large which leads to shift wrapping here.  This means we report
a "block" as supported when it's not, and that leads to array overflows
later on.

This bug is not really a security issue in real life, because debugfs is
generally root only.

Fixes: 36ea1bd2

 ("drm/amdgpu: add debugfs ctrl node")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>