Input: iqs7222 - explicitly define number of external channels

The number of external channels is assumed to be a multiple of 10,
but this is not the case for IQS7222D. As a result, some CRx pins
are wrongly prevented from being assigned to some channels.

Address this problem by explicitly defining the number of external
channels for cases in which the number of external channels is not
equal to the total number of available channels.

Fixes: dd24e202 ("Input: iqs7222 - add support for Azoteq IQS7222D")
Signed-off-by: Jeff LaBundy <jeff@labundy.com>
Link: https://lore.kernel.org/r/aGHVf6HkyFZrzTPy@nixie71


Cc: stable@vger.kernel.org
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>