MIPS: Netlogic: Fix UP compilation on XLR

MIPS: Netlogic: Fix UP compilation on XLR

The commit 2a37b1a "MIPS: Netlogic: Move from u32 cpumask to cpumask_t"
breaks uniprocessor compilation on XLR with:

arch/mips/netlogic/xlr/setup.c: In function 'prom_init':
arch/mips/netlogic/xlr/setup.c:196:6: error: unused variable 'i'

Fix by defining 'i' only when CONFIG_SMP is defined.

Signed-off-by: Jayachandran C <jchandra@broadcom.com>
Patchwork: http://patchwork.linux-mips.org/patch/4760/
Signed-off-by: John Crispin <blogic@openwrt.org>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>