tgsi/ureg: return correct token count in ureg_get_tokens

tgsi/ureg: return correct token count in ureg_get_tokens

Valgrind reports that the shader cache writes uninitialized data to disk.
Turns out ureg_get_tokens() is returning the count of allocated tokens
instead of how many are actually used, so the cache writes out unused
space at the end. Use the real count instead.

This change should not cause regressions elsewhere because the only
ureg_get_tokens() user that cares about token count is the shader cache.

Signed-off-by: Grazvydas Ignotas <notasas@gmail.com>
Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>