hwmon (coretemp): Fix build breakage if SMP is undefined

Commit e40cc4bd introduced
a build breakage if CONFIG_SMP is undefined. This commit
fixes the problem.

This fix is only a workaround. For a real fix, cpu_sibling_mask() should
be defined in UP include code, eg in linux/smp.h, and asm/smp.h should not be
included directly. This fix is currently not possible because asm/smp.h defines
cpu_sibling_mask() unconditionally and is included directly from many source
files.
Reported-by: NIngo Molnar <mingo@elte.hu>
Tested-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NGuenter Roeck <guenter.roeck@ericsson.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>

drivers/hwmon/coretemp.c

@@ -36,6 +36,7 @@
 #include <linux/pci.h>
 #include <asm/msr.h>
 #include <asm/processor.h>
+#include <asm/smp.h>
 
 #define DRVNAME	"coretemp"