x86/RAS: Simplify SMCA bank descriptor struct

Call the struct simply smca_bank, it's instance ID can be simply ->id.
Makes the code much more readable.

Signed-off-by: Borislav Petkov <bp@suse.de>
Tested-by: Yazen Ghannam <yazen.ghannam@amd.com>
Link: http://lkml.kernel.org/r/20161103125556.15482-1-bp@alien8.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>