device-mapper: using EXPORT_SYBOL in dm-space-map-checker.c needs export.h

Reported-by: NWitold Baryluk <baryluk@smp.if.uj.edu.pl>
Signed-off-by: NStephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: NPaul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

drivers/md/persistent-data/dm-space-map-checker.c

@@ -7,6 +7,7 @@
 #include "dm-space-map-checker.h"
 
 #include <linux/device-mapper.h>
+#include <linux/export.h>
 
 #ifdef CONFIG_DM_DEBUG_SPACE_MAPS