drm/amdgpu: fix typo in amdgpu_debugfs_test_ib_init

drm/amdgpu: fix typo in amdgpu_debugfs_test_ib_init

The debugfs interface has calls a function that was evidently
defined under the wrong name in some configurations:

drivers/gpu/drm/amd/amdgpu/amdgpu_device.c:64:12: error: 'amdgpu_debugfs_test_ib_ring_init' used but never defined [-Werror]
drivers/gpu/drm/amd/amdgpu/amdgpu_device.c:3803:12: error: 'amdgpu_debugfs_test_ib_init' defined but not used [-Werror=unused-function]

This fixes the function name.

Fixes: 4f0955fcc052 ("drm/amdgpu: export test ib debugfs interface")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>