If we fail to allocate an indirect buffer (ib) when updating
the ptes, return an error instead of trying to use the ib.
Avoids a null pointer dereference.

Bug:
https://bugzilla.kernel.org/show_bug.cgi?id=58621Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org