xsm/flask: Fix undefined behaviour in avc_dump_av()

When booting Xen with CONFIG_USBAN=y and CONFIG_XSM_FLASK=y,
UBSAN reports undefined behaviour in avc_dump_av() due to a left
shift on a signed int:

(XEN) [    1.104348] ================================================================================
(XEN) [    1.105096] UBSAN: Undefined behaviour in xsm/flask/avc.c:184:14
(XEN) [    1.106052] left shift of 1073741824 by 1 places cannot be represented in type 'int'
(XEN) [    1.107546] Xen WARN at common/ubsan/ubsan.c:176
(XEN) [    1.108295] ----[ Xen-4.21.1  arm64  debug=y ubsan=y  Not tainted ]----
(XEN) [    1.108848] CPU:    0
(XEN) [    1.109147] PC:     00000a00002f64fc ubsan.c#ubsan_epilogue+0x10/0xd4
[...]
(XEN) [    1.146320] Xen call trace:
(XEN) [    1.146663]    [<00000a00002f64fc>] ubsan.c#ubsan_epilogue+0x10/0xd4 (PC)
(XEN) [    1.147227]    [<00000a00002f7bc4>] __ubsan_handle_shift_out_of_bounds+0x1a0/0x290 (LR)
(XEN) [    1.147868]
(XEN) [    1.148177] ================================================================================

This can be solved by making 'perm' an unsigned 32-bit type (u32).

Signed-off-by: Dmytro Prokopchuk <dmytro_prokopchuk1@epam.com>
Acked-by: Daniel P. Smith <dpsmith@apertussolutions.com>

xen/xsm/flask/avc.c

@@ -152,7 +152,8 @@ static void __attribute__ ((format (printf, 2, 3)))
  */
 static void avc_dump_av(struct avc_dump_buf *buf, u16 tclass, u32 av)
 {
-    int i, i2, perm;
+    int i, i2;
+    uint32_t perm;
 
     if ( av == 0 )
     {