xtensa: fix kmap_prot definition

Replace PAGE_KERNEL with PAGE_KERNEL_EXEC to allow copy_to_user_page
invalidate icache for pages mapped with kmap.

Cc: stable@vger.kernel.org
Signed-off-by: NMax Filippov <jcmvbkbc@gmail.com>

arch/xtensa/include/asm/highmem.h

@@ -25,7 +25,7 @@
 #define PKMAP_NR(virt)		(((virt) - PKMAP_BASE) >> PAGE_SHIFT)
 #define PKMAP_ADDR(nr)		(PKMAP_BASE + ((nr) << PAGE_SHIFT))
 
-#define kmap_prot		PAGE_KERNEL
+#define kmap_prot		PAGE_KERNEL_EXEC
 
 #if DCACHE_WAY_SIZE > PAGE_SIZE
 #define get_pkmap_color get_pkmap_color