counter: Add the necessary colons and indents to the comments of counter_compi

Since commit aaec1a0f ("counter: Internalize sysfs interface code")
introduce a warning as:

linux-next/Documentation/driver-api/generic-counter:234: ./include/linux/counter.h:43: WARNING: Unexpected indentation.
linux-next/Documentation/driver-api/generic-counter:234: ./include/linux/counter.h:45: WARNING: Block quote ends without a blank line; unexpected unindent.

Add the necessary colons and indents.

Fixes: aaec1a0f

 ("counter: Internalize sysfs interface code")
Signed-off-by: Yanteng Si <siyanteng@loongson.cn>
Signed-off-by: William Breathitt Gray <vilhelm.gray@gmail.com>
Link: https://lore.kernel.org/r/26011e814d6eca02c7ebdbb92f171a49928a7e89.1640072891.git.vilhelm.gray@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>