IB/ipath: Add missing <linux/stat.h> in ipath_chip_init.c

Fix build errors:

    drivers/infiniband/hw/ipath/ipath_init_chip.c:54:1: error: 'S_IRUGO' undeclared here (not in a function)
    drivers/infiniband/hw/ipath/ipath_init_chip.c:54:1: error: bit-field '<anonymous>' width not an integer constant
    drivers/infiniband/hw/ipath/ipath_init_chip.c:67:1: error: 'S_IWUSR' undeclared here (not in a function)
    drivers/infiniband/hw/ipath/ipath_init_chip.c:67:1: error: bit-field '<anonymous>' width not an integer constant

Signed-off-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Roland Dreier <roland@purestorage.com>