Remove condition which always evaluates to true (size_t >= 0).

Found with -Wtype-limits.

Change-Id: I5580f179425bc6b09ff2a8559fce121b0cc8ae14
Signed-off-by: Piotr Sikora <piotrsikora@google.com>
Reviewed-on: https://boringssl-review.googlesource.com/6463
Reviewed-by: Adam Langley <agl@google.com>

crypto/hmac/hmac.c

diff --git a/crypto/hmac/hmac.c b/crypto/hmac/hmac.c
index d37a249..be2dcce 100644
--- a/crypto/hmac/hmac.c
+++ b/crypto/hmac/hmac.c
@@ -129,7 +129,7 @@
         return 0;
       }
     } else {
-      assert(key_len >= 0 && key_len <= sizeof(key_block));
+      assert(key_len <= sizeof(key_block));
       memcpy(key_block, key, key_len);
       key_block_len = (unsigned)key_len;
     }