ima: sparse fix: include linux/ima.h in ima_main.c

Fixes sparse warnings:
security/integrity/ima/ima_main.c:105:6: warning: symbol 'ima_file_free' was not declared. Should it be static?
security/integrity/ima/ima_main.c:167:5: warning: symbol 'ima_file_mmap' was not declared. Should it be static?
security/integrity/ima/ima_main.c:192:5: warning: symbol 'ima_bprm_check' was not declared. Should it be static?
security/integrity/ima/ima_main.c:211:5: warning: symbol 'ima_file_check' was not declared. Should it be static?

Signed-off-by: James Morris <jmorris@namei.org>

security/integrity/ima/ima_main.c

@@ -22,6 +22,7 @@
 #include <linux/mount.h>
 #include <linux/mman.h>
 #include <linux/slab.h>
+#include <linux/ima.h>
 
 #include "ima.h"