RISC-V: Minor cleanup for s extension support.

Looking at older versions of the patch, I confirmed that the odd comment
I referred to earlier was indeed from the removal of the sx support.  It
also explains an oddly formatted switch statement.  This patch fixes both
minor problems.

	bfd/
	* elfxx-riscv.c (riscv_get_prefix_class): Format s case like others.
	(riscv_parse_prefixed_ext): Fix s extension comment and reword to
	avoid over long line.

Change-Id: I1cb62e4a16188270f029b6376e4b1684000d6c7a

bfd/ChangeLog

@@ -1,3 +1,9 @@
+2020-01-24  Jim Wilson  <jimw@sifive.com>
+
+	* elfxx-riscv.c (riscv_get_prefix_class): Format s case like others.
+	(riscv_parse_prefixed_ext): Fix s extension comment and reword to
+	avoid over long line.
+
 2020-01-24  Nick Clifton  <nickc@redhat.com>
 
 	PR 25447

bfd/elfxx-riscv.c

@@ -1244,9 +1244,7 @@ riscv_get_prefix_class (const char *arch)
 {
   switch (*arch)
     {
-    case 's':
+    case 's': return RV_ISA_CLASS_S;
-      return RV_ISA_CLASS_S;
-
     case 'x': return RV_ISA_CLASS_X;
     case 'z': return RV_ISA_CLASS_Z;
     default: return RV_ISA_CLASS_UNKNOWN;
@@ -1324,8 +1322,8 @@ riscv_parse_prefixed_ext (riscv_parse_subset_t *rps,
 
       /* Check that the name is valid.
 	 For 'x', anything goes but it cannot simply be 'x'.
-	 For 'z', it must be known from a list and also cannot simply be 'z'.
+	 For 's', it must be known from a list and cannot simply be 's'.
-	 For 's', it must be known from a list and also *can* simply be 's'.  */
+	 For 'z', it must be known from a list and cannot simply be 'z'.  */
 
       /* Check that the extension name is well-formed.  */
       if (!config->ext_valid_p (subset))