Tidy ups to the HyperRAM-related assembler

Tidy and explain `get_hyperram_fn_ptr.`
Remove misleading and incorrect comment; this is no return value.

Author: alees24

sw/cheri/common/hyperram_exec_test.S

@@ -1,14 +1,21 @@
 # Copyright lowRISC contributors.
 # Licensed under the Apache License, Version 2.0, see LICENSE for details.
 # SPDX-License-Identifier: Apache-2.0
-.include "assembly-helpers.s"
+	.include "assembly-helpers.s"
 
 	.section .text, "ax", @progbits
 
 	.globl get_hyperram_fn_ptr
 	.p2align 2
-    .type get_hyperram_fn_ptr,@function
+	.type get_hyperram_fn_ptr,@function
+
+// Return an executable capability for the given address; this relies upon pcc containing the
+// supplied address already.
+//
+// entry a0 = address of function
+// return ca0 -> function
 get_hyperram_fn_ptr:
-  auipcc ct0, 0
-  csetaddr ca0, ct0, a0
-  cret
+	auipcc ct0, 0
+	csetaddr ca0, ct0, a0
+	cret
+

sw/cheri/common/hyperram_perf_test.S

@@ -31,7 +31,6 @@
 // ca0 -> destination (word-aligned)
 // ca1 -> source (word-aligned)
 // a2  =  number of bytes to copy
-// return -> beyond destination data.
 hyperram_copy_block:
   srl   a3, a2, 5
   andi  a2, a2, 31  // 0-31 bytes remaining after 32-byte loop.