m48t59: drop obsolete address base arithmetic

Remove now incorrect address base arithmetic, missed by
9936d6e4. Fixes Sparc64 boot.
Signed-off-by: NBlue Swirl <blauwirbel@gmail.com>

hw/m48t59.c

@@ -480,7 +480,6 @@ static void NVRAM_writeb (void *opaque, uint32_t addr, uint32_t val)
 {
     M48t59State *NVRAM = opaque;
 
-    addr -= NVRAM->io_base;
     NVRAM_PRINTF("%s: 0x%08x => 0x%08x\n", __func__, addr, val);
     switch (addr) {
     case 0:
@@ -505,7 +504,6 @@ static uint32_t NVRAM_readb (void *opaque, uint32_t addr)
     M48t59State *NVRAM = opaque;
     uint32_t retval;
 
-    addr -= NVRAM->io_base;
     switch (addr) {
     case 3:
         retval = m48t59_read(NVRAM, NVRAM->addr);