nir: Use _mesa_flsll(InputsRead) in prog->nir.

nir: Use _mesa_flsll(InputsRead) in prog->nir.

InputsRead is a 64-bit bitfield.  Using _mesa_fls would silently
truncate off the high bits, claiming inputs 32..56 (VARYING_SLOT_MAX)
were never read.

Using <= here was a hack I threw in at the last minute to fix programs
which happened to use input slot 32.  Switch back to using < now that
the underlying problem is fixed.

Fixes crashes in "Euro Truck Simulator 2" when using prog->nir, which
uses input slot 33.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Matt Turner <mattst88@gmail.com>