gma500: clean up an excessive and confusing helper

This is a left over from the great clean ups in the past. It's confusing as
it returns an int, yet has one caller that never uses it. The caller already
has all the right private variables local so the entire function can be
replaced by a simple if call.

Signed-off-by: Alan Cox <alan@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20160129193731.8475.47809.stgit@localhost.localdomain
Acked-by: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>