Fixed overflow issue. Code originally meant to truncate the 64 bit integer did not...

Fixed overflow issue. Code originally meant to truncate the 64 bit integer did not work as assembler doesn't "cast" variables like C does. get_cycles() was passing the memory address of a 32 bit unsigned int to the x86 call which required 64 bits of storage space. The extra 32 bits corrupted whatever was on the stack next to the variable.

git-svn-id: svn://localhost/ardour2/branches/2.0-ongoing@3791 d708f5d6-7413-0410-9779-e7cbd77b26cf