Spelling fixes in comments and descriptions, patch by luzpaz.

Differential Revision: https://developer.blender.org/D3668

source/blender/imbuf/intern/dds/DirectDrawSurface.cpp

@@ -1394,7 +1394,7 @@ uint DirectDrawSurface::mipmapSize(uint mipmap) const
 	}
 	else if (header.pf.flags & DDPF_RGB || (header.pf.flags & DDPF_LUMINANCE))
 	{
-		uint pitch = computePitch(w, header.pf.bitcount, 8); // Asuming 8 bit alignment, which is the same D3DX expects.
+		uint pitch = computePitch(w, header.pf.bitcount, 8); // Assuming 8 bit alignment, which is the same D3DX expects.
 
 		return pitch * h * d;
 	}