card_fs_uicc.c: Fix unused compilation warning

This array of bytes is not yet used but is referring to some specs. They
may be used in the future, so leave it there but mark it explicitly as
unused.

Change-Id: I0a61d17f9989ecddafbc68d4b9446853e4c15159
diff --git a/src/sim/card_fs_uicc.c b/src/sim/card_fs_uicc.c
index 70737b6..27afe34 100644
--- a/src/sim/card_fs_uicc.c
+++ b/src/sim/card_fs_uicc.c
@@ -205,4 +205,4 @@
 };
 
 /* Annex E - TS 101 220 */
-static const uint8_t adf_uicc_aid[] = { 0xA0, 0x00, 0x00, 0x00, 0x87, 0x10, 0x01 };
+static const uint8_t __attribute__((__unused__)) adf_uicc_aid[] = { 0xA0, 0x00, 0x00, 0x00, 0x87, 0x10, 0x01 };