[pinmux] Switch to correct parameter in regfile template
[pinmux] Switch to correct parameter in regfile template

The PERIPH_INSEL CSR had the wrong count parameter in its hjson
specification. This commit corrects that and sets the parameter
to `NPeriphIn`.

lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan