wifi-scripts: ucode: iwinfo: skip uninitialized PHYs

wifi-scripts: ucode: iwinfo: skip uninitialized PHYs

They show up as null entries in the nl80211 wiphy dump.
Fixes the following error:

Reference error: left-hand side expression is null
In find_phy(), file /usr/share/ucode/iwinfo.uc, line 19, byte 11:
  called from function get_max_power (/usr/share/ucode/iwinfo.uc:42:32)
  called from function module (/usr/share/ucode/iwinfo.uc:102:39)
  called from anonymous function (/usr/bin/iwinfo:5:25)

 `        if (phy.wiphy == wiphy)`
  Near here ------^

Signed-off-by: Felix Fietkau <nbd@nbd.name>