RAPIDIO: IDT_GEN2: Fix build error.

  CC      drivers/rapidio/switches/idt_gen2.o
drivers/rapidio/switches/idt_gen2.c: In function ‘idtg2_show_errlog’:
drivers/rapidio/switches/idt_gen2.c:379:30: error: ‘PAGE_SIZE’ undeclared (first use in this function)
drivers/rapidio/switches/idt_gen2.c:379:30: note: each undeclared identifier is reported only once for each function it appears in

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Acked-by: Alexandre Bounine <alexandre.bounine@idt.com>