riscv: vector: Fix a typo of preempt_v

The term "preempt_v" represents the RISCV_PREEMPT_V field of riscv_v_flags
and is used in lots of comments.

Here corrects the miss-spelling "prempt_v". And s/acheived/achieved/.

Reviewed-by: Andy Chiu <andybnac@gmail.com>
Signed-off-by: Song Shuai <songshuaishuai@tinylab.org>
Link: https://lore.kernel.org/r/20240221100252.3990445-1-songshuaishuai@tinylab.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

Author: Song Shuai

arch/riscv/include/asm/simd.h

@@ -34,9 +34,9 @@ static __must_check inline bool may_use_simd(void)
 		return false;
 
 	/*
-	 * Nesting is acheived in preempt_v by spreading the control for
+	 * Nesting is achieved in preempt_v by spreading the control for
 	 * preemptible and non-preemptible kernel-mode Vector into two fields.
-	 * Always try to match with prempt_v if kernel V-context exists. Then,
+	 * Always try to match with preempt_v if kernel V-context exists. Then,
 	 * fallback to check non preempt_v if nesting happens, or if the config
 	 * is not set.
 	 */