pd-mapper: Null terminate firmware_value string

Null terminate firmware_value string to prevent
strlen() read past the end of buffer error on AOSP.

Otherwise pd-mapper will crash:
  console:/ # pd-mapper
  FORTIFY: strlen: detected read past end of buffer
  Aborted
  134|console:/ #

Signed-off-by: Amit Pundir <amit.pundir@linaro.org>

pd-mapper.c

@@ -242,6 +242,8 @@ static int pd_enumerate_jsons(struct assoc *json_set)
 			continue;
 		}
 
+		firmware_value[n] = '\0';
+
 		if (strlen(FIRMWARE_BASE) + strlen(firmware_value) + 1 > sizeof(path))
 			continue;