riscv: Kconfig.erratas: Add comments

Add trailing comments to endmenu statements for better readability.
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Link: https://lore.kernel.org/r/20220520120232.148310-3-juergh@canonical.comSigned-off-by: Palmer Dabbelt <palmer@rivosinc.com>

arch/riscv/Kconfig.erratas

@@ -42,4 +42,4 @@ config ERRATA_SIFIVE_CIP_1200
 
 	  If you don't know what to do here, say "Y".
 
-endmenu
+endmenu # "CPU errata selection"