nir: Use VARYING_SLOT_TESS_MAX to size indirect bitmasks

nir: Use VARYING_SLOT_TESS_MAX to size indirect bitmasks

MAX_VARYINGS_INCL_PATCH subtracts VARYING_SLOT_VAR0 giving us a size
that's too small, so BITSET_SET writes words out of bounds, corrupting
the stack and causing all kinds of chaos.  VARYING_SLOT_TESS_MAX is
the right value to use here, as it's the largest location.

Closes: 2002
Fixes: ee2050b1111 ("nir: Use BITSET for tracking varyings in lower_io_arrays")
Reviewed-by: Kristian H. Kristensen <hoegsberg@google.com>