Add extra braces for uintNNxMx4_t initializers.

These structs are always implemented as
    struct uintNNxMx4_t {
        uintNNxM val[4];
    };
So, the first set of braces is for the struct, the second for val.

BUG=skia:

Review URL: https://codereview.chromium.org/1221453002
1 file changed