ntb_hw_switchtec: Fix shift-out-of-bounds in switchtec_ntb_mw_set_trans

There is a kernel API ntb_mw_clear_trans() would pass 0 to both addr and
size. This would make xlate_pos negative.

[ 23.734156] switchtec switchtec0: MW 0: part 0 addr 0x0000000000000000 size 0x0000000000000000
[ 23.734158] ================================================================================
[ 23.734172] UBSAN: shift-out-of-bounds in drivers/ntb/hw/mscc/ntb_hw_switchtec.c:293:7
[ 23.734418] shift exponent -1 is negative

Ensuring xlate_pos is a positive or zero before BIT.

Fixes: 1e2fd202f859 ("ntb_hw_switchtec: Check for alignment of the buffer in mw_set_trans()")
Signed-off-by: Yajun Deng <[e-mail]>
Reviewed-by: Logan Gunthorpe <[e-mail]>
Signed-off-by: Jon Mason <[e-mail]>

drivers/ntb/hw/mscc/ntb_hw_switchtec.c

···
 	if (size != 0 && xlate_pos < 12)
 		return -EINVAL;
 
-	if (!IS_ALIGNED(addr, BIT_ULL(xlate_pos))) {
+	if (xlate_pos >= 0 && !IS_ALIGNED(addr, BIT_ULL(xlate_pos))) {
 		/*
 		 * In certain circumstances we can get a buffer that is
 		 * not aligned to its size. (Most of the time