radv: fix emitting descriptor pointers with LLVM < 7

radv: fix emitting descriptor pointers with LLVM < 7

This was terribly wrong, I forced use of 32-bit pointers when
emitting shader descriptor pointers. This fixes GPU hangs with
LLVM 5&6 because 32-bit pointers are only supported with LLVM 7.

Fixes: 88d1ed0f81 ("radv: emit shader descriptor pointers consecutively")
Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>