gianfar driver: eliminate compiler warnings and unnecessary macros

This patch eliminates the warning of unused return values when the driver
registers it sysfs files.  Now the driver will print an error if it is
unable to register the sysfs files.

It also eliminates the macros used to wrap the DEVICE_ATTR macro and the
device_create_file function call.  The macros don't reduce the number of
lines of source code in the file and the name munging makes is so that
cscope and friends don't see the references to the functions.  It's better
to just call the kernel API directly.

While we're at it, the DEVICE_ATTR instances have been moved down to
be grouped with the functions they depend on.

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Jeff Garzik <jeff@garzik.org>