DPP: Silence a compiler warning on signed/unsigned comparison

Signed-off-by: Jouni Malinen <jouni@codeaurora.org>
diff --git a/dpp.c b/dpp.c
index 109ae0e..0222047 100644
--- a/dpp.c
+++ b/dpp.c
@@ -258,7 +258,7 @@
 			int pass_len;
 
 			pass_len = parse_hexstr(pos, (u8 *) pass, sizeof(pass));
-			if (pass_len < 0 || pass_len >= sizeof(pass))
+			if (pass_len < 0 || (size_t) pass_len >= sizeof(pass))
 				return -2;
 			pass[pass_len] = '\0';
 			sigma_dut_print(dut, DUT_MSG_INFO,