Adapt the suggestions for the assembly string functions that Andrew
suggested but that I didn't manage to include into the series that
got applied.

This includes improvements to two comments, removal of unneeded labels
and moving one instruction slightly higher to contradict an
explanatory comment.
Suggested-by: NAndrew Jones <ajones@ventanamicro.com>
Signed-off-by: NHeiko Stuebner <heiko.stuebner@vrull.eu>
Reviewed-by: NAndrew Jones <ajones@ventanamicro.com>
Tested-by: NConor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20230208225328.1636017-3-heiko@sntech.deSigned-off-by: NPalmer Dabbelt <palmer@rivosinc.com>