Fix a few ShellCheck reported warnings from PR #213

The checks on the upstream project have reported some warnings to the
code accepted in PR #213, fix them in this commit.

Signed-off-by: Marco Chiappero <marco.chiappero@suse.com>

ironic-image/scripts/ironic-common.sh

@@ -85,7 +85,7 @@ get_interface_of_ip()
     # For IPv6 addresses, this will give the short-form address
     IP_ADDR="$(ipcalc "${IP_ADDR}" | grep "^Address:" | awk '{print $2}')"
 
-    echo $(ip "${IP_VERS}" -br addr show scope global | grep -i " ${IP_ADDR}/" | cut -f 1 -d ' ' | cut -f 1 -d '@')
+    echo $(ip ${IP_VERS} -br addr show scope global | grep -i " ${IP_ADDR}/" | cut -f 1 -d ' ' | cut -f 1 -d '@')
 }
 
 get_ip_of_interface()
@@ -111,7 +111,7 @@ get_ip_of_interface()
 
     local IFACE=$1
 
-    echo $(ip "${IP_VERS}" -br addr show scope global up dev ${IFACE} | awk '{print $3}' | sed -e 's%/.*%%' | head -n 1)
+    echo $(ip ${IP_VERS} -br addr show scope global up dev ${IFACE} | awk '{print $3}' | sed -e 's%/.*%%' | head -n 1)
 }
 
 get_provisioning_interface()