anv: Drop const on anv_framebuffer::attachments
anv: Drop const on anv_framebuffer::attachments

The attachments should be const, but the driver's function signatures
are generally not const-friendly.

Drop the const because it conflicts with upcoming
anv_cmd_buffer_resolve_subpass().

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler