Changes

ctl: When setting Sa bits, other bits must remain set to '1'

Some of the other bits will be used 'as-is'.
For instance the bit 0 (MSB) will be copied from this if operating
in nocrc4 mode.

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
Change-Id: Id482c6a114e7bf051d157e81038f015e9d26fa99