drm/i915: Fixup kerneldoc for intel_uc_fw_upload()

Just a parameter name change that was lost to kerneldoc.

drivers/gpu/drm/i915/intel_uc_fw.c:209: warning: Function parameter or member 'xfer' not described in 'intel_uc_fw_upload'
drivers/gpu/drm/i915/intel_uc_fw.c:209: warning: Excess function parameter 'loader' description in 'intel_uc_fw_upload'

v2: Add the Returns:

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180214105332.30230-1-chris@chris-wilson.co.uk