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>
diff --git a/drivers/net/zynq_gem.c b/drivers/net/zynq_gem.c
index 74fda70..c723dbb 100644
--- a/drivers/net/zynq_gem.c
+++ b/drivers/net/zynq_gem.c
@@ -513,7 +513,8 @@
 
 	/* 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;