MIPS: Malta: Fix GCC 4.6.0 build error

  CC      arch/mips/mti-malta/malta-int.o
arch/mips/mti-malta/malta-int.c: In function 'mips_pcibios_iack':
arch/mips/mti-malta/malta-int.c:59:6: error: variable 'dummy' set but not used [-Werror=unused-but-set-variable]
cc1: all warnings being treated as errors

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>