glsl: Initialize ir_to_mesa_visitor members in constructor.

Fix defects reported by Coverity Scan.

Uninitialized pointer field (UNINIT_CTOR) uninit_member: Non-static class member ctx is not initialized in this constructor nor in any functions that it calls. uninit_member: Non-static class member prog is not initialized in this constructor nor in any functions that it calls. uninit_member: Non-static class member shader_program is not initialized in this constructor nor in any functions that it calls. uninit_member: Non-static class member options is not initialized in this constructor nor in any functions that it calls.

Signed-off-by: Vinson Lee vlee@freedesktop.org