internal/bytealg: fix riscv64 offset names

Vet caught that these were incorrect.

Updates #37022

Change-Id: I7b5cd8032ea95eb8e0729f6a4f386aec613c71d8
Reviewed-on: https://go-review.googlesource.com/c/go/+/217777
Run-TryBot: Josh Bleecher Snyder <[email protected]>
Reviewed-by: Cherry Zhang <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>

Author: josharian

src/internal/bytealg/indexbyte_riscv64.s

@@ -6,8 +6,8 @@
 #include "textflag.h"
 
 TEXT ·IndexByte(SB),NOSPLIT,$0-40
-	MOV	s+0(FP), A1
-	MOV	s_len+8(FP), A2
+	MOV	b_base+0(FP), A1
+	MOV	b_len+8(FP), A2
 	MOVBU	c+24(FP), A3	// byte to find
 	MOV	A1, A4		// store base for later
 	ADD	A1, A2		// end
@@ -29,8 +29,8 @@ notfound:
 	RET
 
 TEXT ·IndexByteString(SB),NOSPLIT,$0-32
-	MOV	p+0(FP), A1
-	MOV	b_len+8(FP), A2
+	MOV	s_base+0(FP), A1
+	MOV	s_len+8(FP), A2
 	MOVBU	c+16(FP), A3	// byte to find
 	MOV	A1, A4		// store base for later
 	ADD	A1, A2		// end