drm/i915: enum i915_power_well_id is not proper kernel-doc

Revert to a normal comment, as the enum isn't properly documented
anyway.
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/f2c44a0aa00ea7d9b71e7a3183a7507f98811146.1502368010.git.jani.nikula@intel.com

drivers/gpu/drm/i915/i915_reg.h

@@ -1127,7 +1127,7 @@ static inline bool i915_mmio_reg_valid(i915_reg_t reg)
 #define   DP_SSS_RESET(pipe)			_DP_SSS(0x2, (pipe))
 #define   DP_SSS_PWR_GATE(pipe)			_DP_SSS(0x3, (pipe))
 
-/**
+/*
  * i915_power_well_id:
  *
  * Platform specific IDs used to look up power wells and - except for custom