The bottom two bits of the simd value were being put into
the upper bits of the wave value which was likely working due
to the bits being ignored (or aliased).

Eitherway, now we mask it correctly.

(v2) Touch up using GENMASK_ULL to a couple of other functions too
Signed-off-by: Tom St Denis <tom.stdenis@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>