drm/i915: fix semicolon.cocci warnings

drivers/gpu/drm/i915/i915_debugfs.c:4850:2-3: Unneeded semicolon

 Removes unneeded semicolon.

Generated by: scripts/coccinelle/misc/semicolon.cocci

CC: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>