arch: c6x: mm: include "asm/uaccess.h" to pass compiling

Need include "asm/uaccess.h" to pass compiling.

The related error (with allmodconfig):
arch/c6x/mm/init.c: In function ‘paging_init’:
arch/c6x/mm/init.c:46:2: error: implicit declaration of function ‘set_fs’ [-Werror=implicit-function-declaration] arch/c6x/mm/init.c:46:9: error: ‘KERNEL_DS’ undeclared (first use in this function) arch/c6x/mm/init.c:46:9: note: each undeclared identifier is reported only once for each function it appears in

---
 arch/c6x/mm/init.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

index e524fde..63f5560 100644
@@ -18,6 +18,7 @@
 #include <linux/initrd.h>
 
 #include <asm/sections.h>
+#include <asm/uaccess.h>
 
 /*
  * ZERO_PAGE is a special page that is used for zero-initialized

1.7.7.6