[ARM] iop: add missing parens in macro

Fix:

 drivers/serial/8250.c:1837: warning: suggest parentheses around arithmetic in operand of |

due to a macro argument being used without required parenthesis.
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

include/asm-arm/hardware/iop3xx.h

@@ -42,7 +42,7 @@ extern int init_atu;
 					IOP3XX_PERIPHERAL_SIZE - 1)
 #define IOP3XX_PERIPHERAL_UPPER_VA (IOP3XX_PERIPHERAL_VIRT_BASE +\
 					IOP3XX_PERIPHERAL_SIZE - 1)
-#define IOP3XX_PMMR_PHYS_TO_VIRT(addr) (u32) ((u32) addr -\
+#define IOP3XX_PMMR_PHYS_TO_VIRT(addr) (u32) ((u32) (addr) -\
 					(IOP3XX_PERIPHERAL_PHYS_BASE\
 					- IOP3XX_PERIPHERAL_VIRT_BASE))
 #define IOP3XX_REG_ADDR(reg)		(IOP3XX_PERIPHERAL_VIRT_BASE + (reg))