can: fix CAN BCM build with CONFIG_PROC_FS disabled

can: fix CAN BCM build with CONFIG_PROC_FS disabled

The introduced namespace support moved the BCM variables for procfs into a
per-net data structure. This leads to a build failure with disabled procfs:

on x86_64:

when CONFIG_PROC_FS is not enabled:

../net/can/bcm.c:1541:14: error: 'struct netns_can' has no member named 'bcmproc_dir'
../net/can/bcm.c:1601:14: error: 'struct netns_can' has no member named 'bcmproc_dir'
../net/can/bcm.c:1696:11: error: 'struct netns_can' has no member named 'bcmproc_dir'
../net/can/bcm.c:1707:15: error: 'struct netns_can' has no member named 'bcmproc_dir'

http://marc.info/?l=linux-can&m=149321842526524&w=2

Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>