staging: comedi: drivers: Fix spelling mistake "nubmer" -> "number"

There is a spelling mistake in a comment. Fix it.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Link: https://lore.kernel.org/r/20210407111301.486853-1-colin.king@canonical.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>