net: gem: Use correct type for casting

Use phys_addr_t which is used in function prototype
in system.h.

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

drivers/net/zynq_gem.c

@@ -513,7 +513,8 @@ int zynq_gem_initialize(bd_t *bis, phys_addr_t base_addr,
 
 	/* Align bd_space to 1MB */
 	bd_space = memalign(1 << MMU_SECTION_SHIFT, BD_SPACE);
-	mmu_set_region_dcache_behaviour((u32)bd_space, BD_SPACE, DCACHE_OFF);
+	mmu_set_region_dcache_behaviour((phys_addr_t)bd_space,
+					BD_SPACE, DCACHE_OFF);
 
 	/* Initialize the bd spaces for tx and rx bd's */
 	priv->tx_bd = (struct emac_bd *)bd_space;