riscv64: use L() in the handful of places we didn't already.

Change-Id: If34ae7a0eb3f7d0bd84018de4b987fd437decf58
diff --git a/libc/arch-riscv64/bionic/syscall.S b/libc/arch-riscv64/bionic/syscall.S
index 1a6e60a..ca735c7 100644
--- a/libc/arch-riscv64/bionic/syscall.S
+++ b/libc/arch-riscv64/bionic/syscall.S
@@ -44,10 +44,10 @@
 
   // Did it fail?
   li a7, -MAX_ERRNO
-  bgtu a0, a7, 1f
-
+  bgtu a0, a7, L(failure)
   ret
-1:
+
+L(failure):
   neg a0, a0
   tail __set_errno_internal
 END(syscall)