wpa_supplicant.sh: always use parameters from the current section

wpa_supplicant.sh: always use parameters from the current section

Using variables from the outer scope unnecessarily complicates the code and
leads to issues.

This patch fixes the bug when having an "adhoc" wifi-iface section before a
"sta" section prevents wpa_supplicant from using the key specified in the
corresponding section as it tries to use the "adhoc" key instead (1 by
default).

Signed-off-by: Paul Fertser <fercerpav@gmail.com>
Backport of r34716

git-svn-id: svn://svn.openwrt.org/openwrt/branches/attitude_adjustment@34717 3c298f89-4303-0410-b956-a3cf2f4a3e73