gallium/u_blitter: Fix a few uninitialized fb_state
What does this MR do and why?
gallium/u_blitter: Fix a few uninitialized fb_state
An uninitialized pipe_framebuffer_state maybe causes some issues
if someone is about to use its members such as `fb_state.layers`.
Signed-off-by: Luc Ma <luc@sietium.com>
Reported-by: Mark Zhou <mark@sietium.com>