SUNRPC: clean up integer overflow check

This integer overflow check works as intended but Clang and GCC and warn
about it when compiling with W=1.

include/linux/sunrpc/xdr.h:539:17: error: comparison is always false
due to limited range of data type [-Werror=type-limits]

Use size_mul() to prevent the integer overflow. It silences the warning
and it's cleaner as well.

Reported-by: Dmitry Antipov <[e-mail]>
Closes: https://lore.kernel.org/all/[e-mail]/
Signed-off-by: Dan Carpenter <[e-mail]>
Acked-by: Jeff Layton <[e-mail]>
Signed-off-by: Anna Schumaker <[e-mail]>

include/linux/sunrpc/xdr.h

···
 
 	if (unlikely(xdr_stream_decode_u32(xdr, &len) < 0))
 		return -EBADMSG;
-	if (len > SIZE_MAX / sizeof(*p))
-		return -EBADMSG;
-	p = xdr_inline_decode(xdr, len * sizeof(*p));
+	p = xdr_inline_decode(xdr, size_mul(len, sizeof(*p)));
 	if (unlikely(!p))
 		return -EBADMSG;
 	if (array == NULL)