i2c: Blackfin TWI: fix REPEAT START mode doesn't repeat

i2c: Blackfin TWI: fix REPEAT START mode doesn't repeat

Avoid rewrite TWI MASTER_CTL reg when issue next message
In i2c repeat transfer mode, byte count of next message should be filled
into part of the TWI MASTER_CTL reg when interrupt MCOMP of last
message transfer is triggered. But, other bits in this reg should
not be touched.

Signed-off-by: Sonic Zhang <[email protected]>
Signed-off-by: Mike Frysinger <[email protected]>
Signed-off-by: Bryan Wu <[email protected]>
[[email protected]: shorted subject]
Signed-off-by: Ben Dooks <[email protected]>