xtensa: fix access check in csum_and_copy_from_user

Commit d341659f ("xtensa: switch to providing
csum_and_copy_from_user()") introduced access check, but incorrectly
tested dst instead of src.
Fix access_ok argument in csum_and_copy_from_user.

Cc: Al Viro <viro@zeniv.linux.org.uk>
Fixes: d341659f ("xtensa: switch to providing csum_and_copy_from_user()")
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

arch/xtensa/include/asm/checksum.h

@@ -57,7 +57,7 @@ static inline
 __wsum csum_and_copy_from_user(const void __user *src, void *dst,
 				   int len, __wsum sum, int *err_ptr)
 {
-	if (access_ok(dst, len))
+	if (access_ok(src, len))
 		return csum_partial_copy_generic((__force const void *)src, dst,
 					len, sum, err_ptr, NULL);
 	if (len)