drm/amdkfd: fix freeing an unset pointer

clang static analysis reports this problem
kfd_chardev.c:2092:2: warning: 1st function call argument
  is an uninitialized value
        kvfree(bo_privs);
        ^~~~~~~~~~~~~~~~

When bo_buckets alloc fails, it jumps to an error handler
that frees the yet to be allocated bo_privs.  Because
bo_buckets is the first error, return directly.

Fixes: 5ccbb057 ("drm/amdkfd: CRIU Implement KFD checkpoint ioctl")
Signed-off-by: Tom Rix <trix@redhat.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>