eeepc-laptop: simplify how the hwmon device reads values from the EC

The hwmon device uses ec_write() to write values to the EC.  So for
consistency it should use ec_read() to read values.  The extra layers
of indirection used did not add any value.

This may mean we no longer take the ACPI global lock for such reads
(if the EC operation region requires the lock and the EC does not).
But there is no point locking each one-byte read individually, when
write operations do not use the lock at all.

Signed-off-by: Alan Jenkins <alan-jenkins@tuffmail.co.uk>
Signed-off-by: Len Brown <len.brown@intel.com>