DF-2308 I2CREAD exerciser on /dev/iic0
claim: copyout of s->count bytes after a short-but-successful iicbus_read()
       discloses the uninitialized kmalloc tail

E  E1 no-start I2CREAD                rc=-1 errno=22 (expect 22) untouched=YES
E2 I2CSTART(NACK 0x6e)          rc=0 errno=0 (expect -1/2 IIC_ENOACK)
E  E2 after-NACK I2CREAD              rc=-1 errno=22 (expect 22) untouched=YES
E3 I2CSTART(write-dir 0x50)     rc=-1 (expect 0)
E  E3 wrong-direction I2CREAD         rc=-1 errno=22 (expect 22) untouched=YES

S  size=64     groom=1 rc=0 errno=0 pattern_bad=0 marker=no kptr-qwords=0  (all bytes = slave TX pattern)
S  size=256    groom=1 rc=0 errno=0 pattern_bad=0 marker=no kptr-qwords=0  (all bytes = slave TX pattern)
S  size=512    groom=1 rc=0 errno=0 pattern_bad=0 marker=no kptr-qwords=0  (all bytes = slave TX pattern)
S  size=1024   groom=1 rc=0 errno=0 pattern_bad=0 marker=no kptr-qwords=0  (all bytes = slave TX pattern)
S  size=2048   groom=1 rc=0 errno=0 pattern_bad=0 marker=no kptr-qwords=0  (all bytes = slave TX pattern)
S  size=64     groom=0 rc=0 errno=0 pattern_bad=0 marker=no kptr-qwords=0  (all bytes = slave TX pattern)
S  size=256    groom=0 rc=0 errno=0 pattern_bad=0 marker=no kptr-qwords=0  (all bytes = slave TX pattern)
S  size=512    groom=0 rc=0 errno=0 pattern_bad=0 marker=no kptr-qwords=0  (all bytes = slave TX pattern)
S  size=1024   groom=0 rc=0 errno=0 pattern_bad=0 marker=no kptr-qwords=0  (all bytes = slave TX pattern)
S  size=2048   groom=0 rc=0 errno=0 pattern_bad=0 marker=no kptr-qwords=0  (all bytes = slave TX pattern)
S  size=16384  groom=0 rc=0 errno=0 pattern_bad=0 marker=no kptr-qwords=0  (all bytes = slave TX pattern)
S  size=64     groom=1 rc=0 errno=0 pattern_bad=0 marker=no kptr-qwords=0  (all bytes = slave TX pattern)
S  size=256    groom=1 rc=0 errno=0 pattern_bad=0 marker=no kptr-qwords=0  (all bytes = slave TX pattern)
S  size=512    groom=1 rc=0 errno=0 pattern_bad=0 marker=no kptr-qwords=0  (all bytes = slave TX pattern)
S  size=1024   groom=1 rc=0 errno=0 pattern_bad=0 marker=no kptr-qwords=0  (all bytes = slave TX pattern)
S  size=2048   groom=1 rc=0 errno=0 pattern_bad=0 marker=no kptr-qwords=0  (all bytes = slave TX pattern)