s390/disassembler: Use proper format specifiers for operand values

s390/disassembler: Use proper format specifiers for operand values

Treat register numbers as unsigned. Treat signed operand values as
signed.

This resolves multiple instances of the Cppcheck warning:

warning: %i in format string (no. 1) requires 'int' but the argument
  type is 'unsigned int'. [invalidPrintfArgType_sint]

Acked-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Jens Remus <jremus@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>