nv50/ir: Initialize RegAlloc member func in constructor.

Fix defect reported by Coverity Scan.

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

Signed-off-by: Vinson Lee <vlee@freedesktop.org>
Reviewed-by: Karol Herbst <kherbst@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/8568>

src/gallium/drivers/nouveau/codegen/nv50_ir_ra.cpp

@@ -224,7 +224,7 @@ RegisterSet::release(DataFile f, int32_t reg, unsigned int size)
 class RegAlloc
 {
 public:
-   RegAlloc(Program *program) : prog(program), sequence(0) { }
+   RegAlloc(Program *program) : prog(program), func(NULL), sequence(0) { }
 
    bool exec();
    bool execFunc();