bitvec: Fix typo in the csn1 encoding code

We can curse about CSN.1 and 3GPP but I think we want to call
it cursor here.
diff --git a/include/osmocom/core/bitvec.h b/include/osmocom/core/bitvec.h
index 3138226..62e2e7b 100644
--- a/include/osmocom/core/bitvec.h
+++ b/include/osmocom/core/bitvec.h
@@ -45,7 +45,7 @@
 
 /*! \brief structure describing a bit vector */
 struct bitvec {
-	unsigned int cur_bit;	/*!< \brief curser to the next unused bit */
+	unsigned int cur_bit;	/*!< \brief cursor to the next unused bit */
 	unsigned int data_len;	/*!< \brief length of data array in bytes */
 	uint8_t *data;		/*!< \brief pointer to data array */
 };