x86/mce/severity: Fix warning about indented braces

Dan reported compiler warnings about missing curly braces in
mce_severity_amd(). Reindent the catch-all "return MCE_AR_SEVERITY"
correctly to single tab.

While at it, chain ctx == IN_KERNEL check with mcgstatus check to make
it cleaner, as suggested by Boris.

No functional changes are introduced by this patch.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Aravind Gopalakrishnan <Aravind.Gopalakrishnan@amd.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tony Luck <tony.luck@intel.com>
Cc: linux-edac <linux-edac@vger.kernel.org>
Link: http://lkml.kernel.org/r/1427814281-18192-1-git-send-email-Aravind.Gopalakrishnan@amd.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>