compositor-drm: pass NULL to mmap() instead of 0 as the address
compositor-drm: pass NULL to mmap() instead of 0 as the address

mmap() function expects to be passed a void pointer as the address
here. Passing NULL is technically more correct than passing 0.

Signed-off-by: Chris Michael <177aeddb9e34930a357ecd8dd2d21c80fe280c85@samsung.com>
Reviewed-by: Derek Foreman <2f97e0f0bc172406aab8ccd42dab54c95bab8759@osg.samsung.com>

Fantu/compositor-spice,Fantu/compositor-spice,krezovic/weston,sir-murray/weston,giucam/weston,Gnurou/weston,giucam/weston,kwm81/weston,krezovic/weston,Gnurou/weston,Fantu/compositor-spice,sir-murray/weston,kwm81/weston