hal_wifi: Allow HAL to reload wifi firmware

Need write permissions on the specified sysfs path for reloading
firmware.

Denials:
01-21 23:39:01.650  4669  4669 W android.hardwar: type=1400
audit(0.0:103): avc: denied { write } for name="fwpath" dev="sysfs"
ino=6847 scontext=u:r:hal_wifi:s0
tcontext=u:object_r:sysfs_wlan_fwpath:s0 tclass=file permissive=0
01-21 23:39:01.653  4669  4669 E android.hardware.wifi@1.0-service:
Failed to open wlan fw path param: Permission denied

Bug: 32018162
Test: Denials no longer present in the logs.
Change-Id: I1a468e7c2a2a4360a2b61f04f1940471d52d0dd6