Clean up OMAPModifyPixmapHeader
Clean up OMAPModifyPixmapHeader

OMAPModifyPixmapHeader shouldn't call miModifyPixmapHeader directly
since it can reset the pixmap's reference count, causing memory issues
on free (specifically, we saw crashes using the root pixmap). This patch
removes the direct call and cleans up the structure of the function.

commshare/xf86-video-armsoc,singulared/xf86-video-armsoc,commshare/xf86-video-armsoc,mdrjr/xf86-video-armsoc,singulared/xf86-video-armsoc,mmind/xf86-video-armsoc,xin3liang/xf86-video-armsoc,xin3liang/xf86-video-armsoc,Popolon/xf86-video-armsoc,mmind/xf86-video-armsoc,mdrjr/xf86-video-armsoc,sbambrough/xf86-video-armsoc,OtherCrashOverride/armsoc-hardkernel,OtherCrashOverride/armsoc-hardkernel,freedesktop-unofficial-mirror/xorg__driver__xf86-video-armsoc,sbambrough/xf86-video-armsoc,apxii/xf86-video-armsoc,freedesktop-unofficial-mirror/xorg__driver__xf86-video-armsoc,apxii/xf86-video-armsoc,Popolon/xf86-video-armsoc