microblaze: Remove unused variable ram_base

This variable is completely unused that's why remove it.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>

board/xilinx/microblaze-generic/microblaze-generic.c

@@ -24,8 +24,6 @@
 
 DECLARE_GLOBAL_DATA_PTR;
 
-ulong ram_base;
-
 int dram_init_banksize(void)
 {
 	return fdtdec_setup_memory_banksize();