Get number used in the operand
This function returns an immediate number used in the operand
ea - linear address of instruction
n - the operand number
The return values are:
operand is an immediate value => immediate value
operand has a displacement => displacement
operand is a direct memory ref => memory address
operand is a register => register number
operand is a register phrase => phrase number
otherwise => -1
long get_operand_value(long ea, long n);