microblaze: Remove compilation warnings in cache macro

CC      arch/microblaze/kernel/cpu/cache.o
arch/microblaze/kernel/cpu/cache.c: In function '__invalidate_dcache_range_wb':
arch/microblaze/kernel/cpu/cache.c:398: warning: ISO C90 forbids mixed declarations and code
arch/microblaze/kernel/cpu/cache.c: In function '__flush_dcache_range_wb':
arch/microblaze/kernel/cpu/cache.c:509: warning: ISO C90 forbids mixed declara

Signed-off-by: Michal Simek <monstr@monstr.eu>