i82975x_edac: Test nr_pages earlier to save a few CPU cycles

Avoid test nr_pages twice, and initializing some data that won't
be used.

Cleanup patch only.

Reported-by: Aristeu Rozanski Filho <arozansk@redhat.com>
Reviewed-by: Aristeu Rozanski <arozansk@redhat.com>
Cc: Ranganathan Desikan <ravi@jetztechnologies.com>
Cc: "Arvind R." <arvino55@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>