caif-hsi: Removed dead code

Simplify logic and remove dead code.

Signed-off-by: Kim Lilliestierna <kim.xx.lilliestierna@stericsson.com>
Signed-off-by: Sjur Brændeland <sjur.brandeland@stericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>