lib/lcm.c: quiet sparse noise

The symbol 'lcm' is exported to the kernel (EXPORT_SYMBOL_GPL).
Pick up it's definition in <linux/lcm.h> to quiet the sparse noise:

  warning: symbol 'lcm' was not declared. Should it be static?
Signed-off-by: NH Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

lib/lcm.c

 #include <linux/kernel.h>
 #include <linux/gcd.h>
 #include <linux/module.h>
+#include <linux/lcm.h>
 
 /* Lowest common multiple */
 unsigned long lcm(unsigned long a, unsigned long b)