RISC-V: Simplify riscv_csr_address logic on state enable extensions

This commit makes CSR class handling for 'Smstateen' and 'Ssstateen'
extensions simpler using fall-throughs (as used in CSR_CLASS_I{,_32}).

gas/ChangeLog:

	* config/tc-riscv.c (riscv_csr_address): Simplify the logic for
	'Smstateen' and 'Ssstateen' extensions.

gas/config/tc-riscv.c

@@ -1049,9 +1049,10 @@ riscv_csr_address (const char *csr_name,
     case CSR_CLASS_SMAIA:
       extension = "smaia";
       break;
-    case CSR_CLASS_SMSTATEEN:
     case CSR_CLASS_SMSTATEEN_32:
-      is_rv32_only = (csr_class == CSR_CLASS_SMSTATEEN_32);
+      is_rv32_only = true;
+      /* Fall through.  */
+    case CSR_CLASS_SMSTATEEN:
       extension = "smstateen";
       break;
     case CSR_CLASS_SSAIA:
@@ -1064,12 +1065,13 @@ riscv_csr_address (const char *csr_name,
 		       || csr_class == CSR_CLASS_SSAIA_AND_H_32);
       extension = "ssaia";
       break;
-    case CSR_CLASS_SSSTATEEN:
-    case CSR_CLASS_SSSTATEEN_AND_H:
     case CSR_CLASS_SSSTATEEN_AND_H_32:
-      is_rv32_only = (csr_class == CSR_CLASS_SSSTATEEN_AND_H_32);
-      is_h_required = (csr_class == CSR_CLASS_SSSTATEEN_AND_H
-		      || csr_class == CSR_CLASS_SSSTATEEN_AND_H_32);
+      is_rv32_only = true;
+      /* Fall through.  */
+    case CSR_CLASS_SSSTATEEN_AND_H:
+      is_h_required = true;
+      /* Fall through.  */
+    case CSR_CLASS_SSSTATEEN:
       extension = "ssstateen";
       break;
     case CSR_CLASS_SSCOFPMF_32: