riscv: __asm_copy_to-from_user: Fix: Typos in comments

Fixing typos and grammar mistakes and using more intuitive label
name.

Signed-off-by: Akira Tsukamoto <akira.tsukamoto@gmail.com>
Fixes: ca6eaaa2 ("riscv: __asm_copy_to-from_user: Optimize unaligned memory access and pipeline stall")
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>