[IA64] bte_copy of BTE_MAX_XFER trips BUG_ON.

BTE_MAX_XFER is wrong.  It is one greater than the number of cache
lines the BTE is actually able to transfer.  If you request a transfer
of exactly BTE_MAX_XFER size, you trip a very cryptic BUG_ON() which
should certainly be made more clear.

This patch fixes that constant and also cleans up the BUG_ON()s in
arch/ia64/sn/kernel/bte.c to test one condition per line.

Signed-off-by: Robin Holt <holt@sgi.com>
Signed-off-by: Tony Luck <aegl@agluck-desktop.(none)>