nir: fix shfr constant folding with zero src2

No fossil-db changes.

Signed-off-by: Rhys Perry <pendingchaos02@gmail.com>
Reviewed-by: Georg Lehmann <dadschoorse@gmail.com>
Fixes: 08903bbe89 ("nir: add mqsad_4x8, shfr and nir_opt_mqsad")
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/31808>

src/compiler/nir/nir_opcodes.py

@@ -885,8 +885,8 @@ opcode("uror", 0, tuint, [0, 0], [tuint, tuint32], False, "", """
 
 opcode("shfr", 0, tuint32, [0, 0, 0], [tuint32, tuint32, tuint32], False, "", """
    uint32_t rotate_mask = sizeof(src0) * 8 - 1;
-   dst = (src1 >> (src2 & rotate_mask)) |
-         (src0 << (-src2 & rotate_mask));
+   uint64_t src = src1 | ((uint64_t)src0 << 32);
+   dst = src >> (src2 & rotate_mask);
 """)
 
 bitwise_description = """