net: lwm2m: fix NULL deref in plain_text_read_number()

Per Coverity report, we are assigning the value1 and value2
s64_t pointers a value of 0.  Later when we go to use value1
and value2, they are of course ... NULL.

Fix the typos in the initial assignment of 0 to the
references of value1 and value2.

Fixes: #12300
Fixes: #12296

Signed-off-by: Michael Scott <[email protected]>

Author: mike-scott

subsys/net/lib/lwm2m/lwm2m_rw_plain_text.c

@@ -176,9 +176,9 @@ static size_t plain_text_read_number(struct lwm2m_input_context *in,
 	u8_t tmp;
 
 	/* initialize values to 0 */
-	value1 = 0;
+	*value1 = 0;
 	if (value2) {
-		value2 = 0;
+		*value2 = 0;
 	}
 
 	while (in->offset < in->in_cpkt->offset) {