proc: switch /proc/bus/ecard/devices to seq_file interface

Signed-off-by: Alexey Dobriyan <adobriyan@sw.ru>
Acked-by: Russell King <rmk+kernel@arm.linux.org.uk>
Cc: Yani Ioannou <yani.ioannou@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>