anv: Clamping Scissor Rect values in a valid range
On cmd_buffer_emit_scissor(), if VkViewport height or width are set to a value lower than 1.0, y_max or x_max can be attributed negative values, causing an overflow. That leads to ScissorRectangleYMax or ScissorRectangleXMax to be set to values on an unsupported range.
Clamping x_max and y_max in the valid range solves the problem.
Closes: #7471 (closed)