lib: fix pointer of type 'void *' used in arithmetic

Using "void *" in arithmetic causes errors with strict compiler settings:
"error: pointer of type 'void *' used in arithmetic [-Werror=pointer-arith]"

Avoid these by calculating on "char *" where 1-byte data size is assumed.

Signed-off-by: Jukka Laitinen <jukkax@ssrc.tii.ae>
Reviewed-by: Dong Du <Dd_nirvana@sjtu.edu.cn>
Reviewed-by: Xiang W <wxjstz@126.com>
Reviewed-by: Anup Patel <anup@brainfault.org>

lib/sbi/sbi_string.c

@@ -149,8 +149,8 @@ void *sbi_memmove(void *dest, const void *src, size_t count)
 			count--;
 		}
 	} else {
-		temp1 = dest + count - 1;
-		temp2 = src + count - 1;
+		temp1 = (char *)dest + count - 1;
+		temp2 = (char *)src + count - 1;
 
 		while (count > 0) {
 			*temp1-- = *temp2--;