Rename some function parameters from 'register' to 'reg'.

Rename some function parameters from 'register' to 'reg'.

[Porting over relevant part of patch by Chris Peterson for Linux kernel
sources.]

Some function prototypes declare an 'int register' parameter. gcc -W
warns "‘register’ is not at beginning of declaration" because the
compiler thinks the parameter has been marked as a 'register' variable
but the author just wanted to name the parameter "register" (which is a
reserved keyword).