sim: card_fs_usim.c: Fix FID of EF.EXT4

The 3GPP spec document also contains this error at one point, and
it seems I copied it from there :/

Change-Id: I7ad9f491c06f6540747b77017678ee37e6a1550d
diff --git a/src/sim/card_fs_usim.c b/src/sim/card_fs_usim.c
index 9e9fc87..3b33c0f 100644
--- a/src/sim/card_fs_usim.c
+++ b/src/sim/card_fs_usim.c
@@ -161,7 +161,7 @@
 		"Key for hidden phone book entries"),
 	EF_LIN_FIX_N(0x6F4D, SFI_NONE, "EF.BDN", F_OPTIONAL, 15, 32,
 		"Barred Dialling Numbers"),
-	EF_LIN_FIX_N(0x6F4E, SFI_NONE, "EF.EXT4", F_OPTIONAL, 13, 13,
+	EF_LIN_FIX_N(0x6F55, SFI_NONE, "EF.EXT4", F_OPTIONAL, 13, 13,
 		"Extension 4"),
 	EF_LIN_FIX_N(0x6F58, SFI_NONE, "EF.CMI", F_OPTIONAL, 2, 16,
 		"Comparison Method Information"),