Release symbol on error-handling path of ips_get_i915_syms()

In ips_get_i915_syms(), the symbol i915_gpu_busy() is not released
when error occurs.

Signed-off-by: minskey guo <chaohong.guo@intel.com>
Acked-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Matthew Garrett <mjg@redhat.com>