qcacld-3.0: Fix mac_handle test in hdd_set_dwell_time()

Recently change "qcacld-3.0: Use mac_handle_t in wlan_hdd_ioctl"
updated the nomenclature used in HDD. During the implementation of
this change a NULL check of mac_handle in hdd_set_dwell_time() had a
"!" removed, incorrectly changing the logic. Restore the correct logic
for NULL-checking mac_handle.

Change-Id: I2bb8393d5adb3156795b3b722d839812419e4995
CRs-Fixed: 2299812
1 file changed