riscv64: fix return value when errorno is 4095

This issue was discovered by seccomp_seccomp_bpf_riscv_64 test.
Actual output:
[0]code=20 jt=00 jf=00 k=0000
[1]code=15 jt=00 jf=01 k=003F
[2]code=06 jt=00 jf=00 k=51000
[3]code=06 jt=00 jf=00 k=7FFF0000
ret=-4095, errno=0

Expected output:
[o]code=20 jt=00 jf=00 k=0000
[1]code=15 jt=00 jf=01 k=003F
[2]code=06 jt=00 jf=00 k=51000
[3]code=06 jt=00 jf=00 k=7FFF0000
ret=-1, errno=4095

Change-Id: Ieebf5f0d1e2f18e2887c463b58ef7ea05ea52898
Signed-off-by: Mao Han <han_mao@linux.alibaba.com>
Signed-off-by: haocheng.zy <zhangye@linux.alibaba.com>
diff --git a/libc/tools/gensyscalls.py b/libc/tools/gensyscalls.py
index 558b004..4f33777 100755
--- a/libc/tools/gensyscalls.py
+++ b/libc/tools/gensyscalls.py
@@ -88,7 +88,7 @@
     ecall
 
     li      a7, -MAX_ERRNO
-    bgtu    a0, a7, 1f
+    bgeu    a0, a7, 1f
 
     ret
 1: