Good grief already! Your question has been answered here:

http://www.keil.com/discuss/docs/thread4297.htm

And here:

http://www.keil.com/discuss/docs/thread4290.htm

If you want to use the 8-bit CRC, just do it and accept the consequences. If you want to do the right thing and use a 16-bit CRC then there are implementations here, on the Keil site, and all over the Internet. There are versions to calculate it 1 bit at a time, 4 bits in parallel (table-driven), 8 bits in parallel (table driven), and 8 bits in parallel via an inline calculation.