drm/i915/guc: Drop redundant ctx param from kerneldoc

drivers/gpu/drm/i915/intel_guc_submission.c:799: warning: Excess function parameter 'ctx' description in 'guc_client_alloc'

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190711162415.2938-1-chris@chris-wilson.co.uk