kernel/crash_core.c: print timestamp using time64_t

The get_seconds() call returns a 32-bit timestamp on some architectures,
and will overflow in the future.  The newer ktime_get_real_seconds()
always returns a 64-bit timestamp that does not suffer from this problem.

Link: http://lkml.kernel.org/r/20180618150329.941903-1-arnd@arndb.deSigned-off-by: NArnd Bergmann <arnd@arndb.de>
Reviewed-by: NAndrew Morton <akpm@linux-foundation.org>
Cc: Dave Young <dyoung@redhat.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Petr Tesarik <ptesarik@suse.cz>
Cc: Marc-Andr Lureau <marcandre.lureau@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

kernel/crash_core.c

@@ -344,7 +344,7 @@ void crash_save_vmcoreinfo(void)
 	if (vmcoreinfo_data_safecopy)
 		vmcoreinfo_data = vmcoreinfo_data_safecopy;
 
-	vmcoreinfo_append_str("CRASHTIME=%ld\n", get_seconds());
+	vmcoreinfo_append_str("CRASHTIME=%lld\n", ktime_get_real_seconds());
 	update_vmcoreinfo_note();
 }