Quick compiler, aarch64: Insane sanity checker

Fix bit-mask generation used in the sanity checking code
for long division by small constants via multiplication.  The
failing case was a 64-bit wide mask.  The macro was using the
desired width of the result as a shift count - and a left
shift of a 64-bit integer by 64 bits is undefined.

Note that the generated code is correct - it's just the sanity
checking code that was wrong.

Change-Id: Ic6654662f848d3caab2c3b1ef0d92fe2eb9673f4