target-i386: Fix compiler warning

With argument checking for cpu_fprintf, gcc throws this warning:

  CC    i386-softmmu/helper.o
cc1: warnings being treated as errors
/qemu/ar7/target-i386/helper.c: In function ‘cpu_x86_dump_seg_cache’:
/qemu/ar7/target-i386/helper.c:220: error: format not a string literal and no format arguments

The code is correct, but current gcc versions don't detect this.
Therefore the patch rewrites the statement to satisfy the compiler.

Signed-off-by: Stefan Weil <weil@mail.berlios.de>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
