gsm_04_12: fix 04.13 typos

There are two occurrences of "413" in the 04.12 header file.
These are probably typos; correct them to "412".

Signed-off-by: Alex Badea <vamposdecampos@gmail.com>
diff --git a/include/osmocore/protocol/gsm_04_12.h b/include/osmocore/protocol/gsm_04_12.h
index bd9e088..9b1538a 100644
--- a/include/osmocore/protocol/gsm_04_12.h
+++ b/include/osmocore/protocol/gsm_04_12.h
@@ -10,7 +10,7 @@
 #define GSM412_SEQ_TRD_BLOCK		0x2
 #define GSM412_SEQ_FTH_BLOCK		0x3
 #define GSM412_SEQ_FST_SCHED_BLOCK	0x8
-#define GSM413_SEQ_NULL_MSG		0xf
+#define GSM412_SEQ_NULL_MSG		0xf
 
 struct gsm412_block_type {
 	uint8_t	seq_nr : 4,
@@ -19,7 +19,7 @@
 		spare : 1;
 } __attribute__((packed));
 
-struct gsm413_sched_msg {
+struct gsm412_sched_msg {
 	uint8_t beg_slot_nr : 6,
 		type : 2;
 	uint8_t end_slot_nr : 6,