GBE: fix one illegal instruction when replace a uniform dst.

GBE: fix one illegal instruction when replace a uniform dst.

When the dst is a uniform value, we replace it with a vector value, then
copy the vector value back may generate an illegal instruction as below
at address 18:

    (14      )  mov(16)         g124<1>:F       g127.7<0,1,0>:F                 { align1 WE_all 1H };
    (16      )  send(16)        g122<1>:UW      g124<8,8,1>:UD
                data (bti: 1, rgba: 14, SIMD16, legacy, Untyped Surface Read) mlen 2 rlen 2 { align1 WE_all 1H };
    (18      )  mov(1)          g127.6<1>:F     g122<8,8,1>:F                   { align1 WE_all };

This patch could fix this issue and generate correct instruction as below:

    (      14)  mov(16)         g124<1>:UD      g127.7<0,1,0>:UD                { align1 WE_all 1H };
    (      16)  send(16)        g122<1>:UW      g124<8,8,1>:UD
                data (bti: 1, rgba: 14, SIMD16, legacy, Untyped Surface Read) mlen 2 rlen 2 { align1 WE_all 1H };
    (      18)  mov(1)          g127.6<1>:UD    g122<0,1,0>:UD                  { align1 WE_all };

Signed-off-by: Zhigang Gong <zhigang.gong@intel.com>
Reviewed-by: "Yang, Rong R" <rong.r.yang@intel.com>