compression: Fix writing output flags

compression: Fix writing output flags

If indic_bit == 0, the shift amount of 32 - indic_bit == 32 will equal
the width of a 32-bit integer type, and these shifts will invoke
undefined behaviour, which is likely to cause incorrect output. Fix this
by not shifting a 32-bit integer type by 32 bits or more.

Signed-off-by: Joseph Sutton <josephsutton@catalyst.net.nz>
Reviewed-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>