staging: comedi: addi_eeprom: cleanup i_EepromReadMainHeader()

Consolidate the two loops used to read the main header data and the
individual function header data from the eeprom.

The structs used to read the main header are not used outside this
function so remove them by reading the eeprom data into local
variables used in the loop.

Consolidate the 'timer' function cases.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>