Fix sub-register number of an address register encoding

Fix sub-register number of an address register encoding

The AddrSubRegNum field in the instruction binary code should be:
  code    value(advanced_flag==0)   value(advanced_flag==1)
  a0.0             0                         0
  a0.1        invalid input                  1
  a0.2             1                         2
  a0.3        invalid input                  3
  a0.4             2                         4
  a0.5        invalid input                  5
  a0.6             3                         6
  a0.7        invalid input                  7
  a0.8             4                  invalid input
  a0.10            5                  invalid input
  a0.12            6                  invalid input
  a0.14            7                  invalid input