he_spr_ie_elem is dereferenced before the NULL check. fix this by moving
the assignment after the check.

fixes commit 697f6c50 ("mac80211: propagate HE operation info into
bss_conf")

This was reported by the static code checker.
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: John Crispin <john@phrozen.org>
Link: https://lore.kernel.org/r/20190813070712.25509-1-john@phrozen.orgSigned-off-by: Johannes Berg <johannes.berg@intel.com>