anv: do not dereference VkPipelineMultisampleStateCreateInfo always
VkGraphicsPipelineCreateInfo.pMultisampleState is a pointer to a VkPipelineMultisampleStateCreateInfo structure, and is ignored if the pipeline has rasterization disabled.
Fixes a crash in one CTS tests that checks this.
Signed-off-by: Samuel Iglesias Gonsálvez siglesias@igalia.com