MIPS: BCM63xx: fix 6328 boot selection bit

MISC_STRAP_BUS_BOOT_SEL_SHIFT is 18 according to Broadcom's GPL source code.
Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

arch/mips/include/asm/mach-bcm63xx/bcm63xx_regs.h

@@ -1367,8 +1367,8 @@
 #define MISC_STRAPBUS_6328_REG		0x240
 #define STRAPBUS_6328_FCVO_SHIFT	7
 #define STRAPBUS_6328_FCVO_MASK		(0x1f << STRAPBUS_6328_FCVO_SHIFT)
-#define STRAPBUS_6328_BOOT_SEL_SERIAL	(1 << 28)
-#define STRAPBUS_6328_BOOT_SEL_NAND	(0 << 28)
+#define STRAPBUS_6328_BOOT_SEL_SERIAL	(1 << 18)
+#define STRAPBUS_6328_BOOT_SEL_NAND	(0 << 18)
 
 /*************************************************************************
  * _REG relative to RSET_PCIE