i82975x_edac: Fix dimm label initialization

The driver has only 4 hardcoded labels, but allows much more memory.
Fix it by removing the hardcoded logic, using snprintf() instead.

[   19.833972] general protection fault: 0000 [#1] SMP
[   19.837733] Modules linked in: i82975x_edac(+) edac_core firewire_ohci firewire_core crc_itu_t nouveau mxm_wmi wmi video i2c_algo_bit drm_kms_helper ttm drm i2c_core
[   19.837733] CPU 0
[   19.837733] Pid: 390, comm: udevd Not tainted 3.6.1-1.fc17.x86_64.debug #1 Dell Inc.                 Precision WorkStation 390    /0MY510
[   19.837733] RIP: 0010:[<ffffffff813463a8>]  [<ffffffff813463a8>] strncpy+0x18/0x30
[   19.837733] RSP: 0018:ffff880078535b68  EFLAGS: 00010202
[   19.837733] RAX: ffff880069fa9708 RBX: ffff880078588000 RCX: ffff880069fa9708
[   19.837733] RDX: 000000000000001f RSI: 5f706f5f63616465 RDI: ffff880069fa9708
[   19.837733] RBP: ffff880078535b68 R08: ffff880069fa9727 R09: 000000000000fffe
[   19.837733] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000003
[   19.837733] R13: 0000000000000000 R14: ffff880069fa9290 R15: ffff880079624a80
[   19.837733] FS:  00007f3de01ee840(0000) GS:ffff88007c400000(0000) knlGS:0000000000000000
[   19.837733] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   19.837733] CR2: 00007f3de00b9000 CR3: 0000000078dbc000 CR4: 00000000000007f0
[   19.837733] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[   19.837733] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
[   19.837733] Process udevd (pid: 390, threadinfo ffff880078534000, task ffff880079642450)
[   19.837733] Stack:
[   19.837733]  ffff880078535c18 ffffffffa017c6b8 00040000816d627f ffff880079624a88
[   19.837733]  ffffc90004cd6000 ffff880079624520 ffff88007ac21148 0000000000000000
[   19.837733]  0000000000000000 0004000000000000 feda000078535bc8 ffffffff810d696d
[   19.837733] Call Trace:
[   19.837733]  [<ffffffffa017c6b8>] i82975x_init_one+0x2e6/0x3e6 [i82975x_edac]
...

Fix bug reported at:
	https://bugzilla.redhat.com/show_bug.cgi?id=848149
And, very likely:
	https://bbs.archlinux.org/viewtopic.php?id=148033
	https://bugzilla.kernel.org/show_bug.cgi?id=47171

Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>