fix section header out of sequence warnings:

```
asciidoctor: WARNING: riscv-zabha.adoc: line 53: section title out of sequence: expected levels 0 or 1, got level 2
asciidoctor: WARNING: riscv-zabha.adoc: line 63: section title out of sequence: expected levels 0 or 1, got level 2
```

Signed-off-by: Kevin Broch <kbroch@rivosinc.com>

src/riscv-zabha.adoc

@@ -1,4 +1,4 @@
-[[header]]
+= Byte and Halfword Atomic Memory Operations (Zabha)
 :description: Byte and Halfword Atomic Memory Operations (Zabha)
 :company: RISC-V.org
 :revdate: 1/2024
@@ -35,7 +35,6 @@ endif::[]
 :footnote:
 :xrefstyle: short
 
-= Byte and Halfword Atomic Memory Operations (Zabha)
 
 // Preamble
 [WARNING]
@@ -50,7 +49,7 @@ likely not conform to the future standard.
 ====
 
 [preface]
-=== Copyright and license information
+== Copyright and license information
 
 This specification is licensed under the Creative Commons
 Attribution 4.0 International License (CC-BY 4.0). The full
@@ -60,7 +59,7 @@ https://creativecommons.org/licenses/by/4.0/.
 Copyright 2024 by RISC-V International.
 
 [preface]
-=== Contributors
+== Contributors
 
 This RISC-V specification has been contributed to directly or indirectly by:
 Ved Shanbhogue, Andrew Waterman, Gianluca Guida, Hans Boehm