rtc_linux.c: Remove useless assignment error = -1;

The Clang static analyzer scan-build from Debian clang version 3.4-1
found the following unneeded assignment.

        rtc_linux.c:756:5: warning: Value stored to 'error' is never read
            error = 1;
            ^       ~

Indeed, if in that if branch, the function returns without ever looking
at the variable `error`. So remove the line.

rtc_linux.c

@@ -753,7 +753,6 @@ read_from_device(void *any)
     /* This looks like a bad error : the file descriptor was indicating it was
      * ready to read but we couldn't read anything.  Give up. */
     LOG(LOGS_ERR, LOGF_RtcLinux, "Could not read flags %s : %s", CNF_GetRtcDevice(), strerror(errno));
-    error = 1;
     SCH_RemoveInputFileHandler(fd);
     switch_interrupts(0); /* Likely to raise error too, but just to be sure... */
     close(fd);