Fix intermittent assert failures in lutpack functions

[gigeresk]

The assert on line 200 causes intermittent failures for FPGA flows (as seen here). The assert is checking that pData doesn't hold a "small integer value" (<= 0xFFFF) which is a valid defensive check.
However, the check casts pData (8B on 64-bit) through ABC_PTRUINT_T to unsigned, which truncates the high 32 bits.
When pData is a valid pointer to data allocated at or above 4 GB boundaries, this assert is triggered because the high bits are non-zero but the lower 32 bits can be near zero.
This fix preserves the original intent and is safe on 32-bit and 64-bit platforms.