aicasm: Correct logic bug in the undefined register bit access detection code.

aicasm: Correct logic bug in the undefined register bit access detection code.

Quoting FreeBSD's commit msg:

The code in question verifies that all register write operations only change
bits that are defined (in the register definition file) for that effected
register.  The bug effectively disabled this checking.

o Fix the check by testing the opcode against all supported read ("and" based)
  operands.

o Add missing bit definitions to the aic7xxx and aic79xx register definition
  files so that the warning (treated as a fatal error) does not spuriously
  fire.

Taken-from: FreeBSD

[While I'm here, also add a missing free() and raise WARNS to 6.]