wifi: zd1211rw: silence sparse warnings

This code wants to compare the obtained value, but as it also
has a special type for register addresses to find places doing
such compares and calculations wrong, we need explicit casts
here to silence sparse.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://msgid.link/20240223114023.976fcd59e97a.I0bba4ef7dc2847ce8ab5ec229149e1a09413b8b9@changeid