MIPS: bcm47xx: Include missing errno.h for ENXIO

Fixes the following build problen on allmodconfig:

arch/mips/bcm47xx/board.c: In function 'bcm47xx_board_detect':
arch/mips/bcm47xx/board.c:291:14: error: 'ENXIO' undeclared
(first use in this function)
Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/6571/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/bcm47xx/board.c

+#include <linux/errno.h>
 #include <linux/export.h>
 #include <linux/string.h>
 #include <bcm47xx_board.h>