Appease GCC's uninitialized value warning.

GCC notices that one function believes < 0 is the error while the other
believes it's != 0. unw_get_reg never returns positive, but match them.

Change-Id: I40af614e6b1400bf3d398bd32beb6d3ec702bc11
Reviewed-on: https://boringssl-review.googlesource.com/c/34985
Reviewed-by: Adam Langley <agl@google.com>
Commit-Queue: Adam Langley <agl@google.com>

crypto/test/abi_test.cc

diff --git a/crypto/test/abi_test.cc b/crypto/test/abi_test.cc
index ed6a2f8..9844c73 100644
--- a/crypto/test/abi_test.cc
+++ b/crypto/test/abi_test.cc
@@ -446,7 +446,7 @@
   int GetReg(crypto_word_t *out, unw_regnum_t reg) {
     unw_word_t val;
     int ret = unw_get_reg(&cursor_, reg, &val);
-    if (ret == 0) {
+    if (ret >= 0) {
       static_assert(sizeof(crypto_word_t) == sizeof(unw_word_t),
                     "crypto_word_t and unw_word_t are inconsistent");
       *out = val;