nvidia: fix sparse warnings

Fix this sparse warnings:

  drivers/video/nvidia/nv_accel.c:304:3: warning: returning void-valued expression
  drivers/video/nvidia/nv_accel.c:323:3: warning: returning void-valued expression

Signed-off-by: Hannes Eder <hannes@hanneseder.net>
Cc: Krzysztof Helt <krzysztof.h1@poczta.fm>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>