Mark input parameter to bitvec_set_bits() as 'const'

The input data is accessed in a read-only manner, so it should be marked
with the const qualifier.

Change-Id: I0d6b86289fa647594f3da1f1c0e0168685307a37
diff --git a/src/bitvec.c b/src/bitvec.c
index 88343c4..ef8fd0e 100644
--- a/src/bitvec.c
+++ b/src/bitvec.c
@@ -198,7 +198,7 @@
  *  \param[in] bits array of \ref bit_value
  *  \param[in] count number of bits to set
  *  \return 0 on success; negative in case of error */
-int bitvec_set_bits(struct bitvec *bv, enum bit_value *bits, unsigned int count)
+int bitvec_set_bits(struct bitvec *bv, const enum bit_value *bits, unsigned int count)
 {
 	int i, rc;