FROMLIST: selftests/vDSO: change elf_hash parameter to signed char

Fixes clang compilation warnings by changing elf_hash's parameter type
to char * and casting to unsigned char * inside elf_hash:

parse_vdso.c:206:22: warning: passing 'const char *' to parameter of
 type 'const unsigned char *' converts between pointers to integer types
 where one is of the unique plain 'char' type and the other is not
 [-Wpointer-sign]
        ver_hash = elf_hash(version);
                            ^~~~~~~
parse_vdso.c:59:52: note: passing argument to parameter 'name' here
static unsigned long elf_hash(const unsigned char *name)
                                                   ^
parse_vdso.c:207:46: warning: passing 'const char *' to parameter of
 type 'const unsigned char *' converts between pointers to integer types
 where one is of the unique plain 'char' type and the other is not
 [-Wpointer-sign]
        ELF(Word) chain = vdso_info.bucket[elf_hash(name) % vdso_info.nbucket];
                                                    ^~~~
parse_vdso.c:59:52: note: passing argument to parameter 'name' here
static unsigned long elf_hash(const unsigned char *name)

Fixes: 98eedc3a9d ("Document the vDSO and add a reference parser")
Change-Id: I163a292875df97c51fa91fc930462d2e9c2c0b13
Signed-off-by: Edward Liaw <edliaw@google.com>
Link: https://lore.kernel.org/all/20240506181951.1804451-1-edliaw@google.com/

tools/testing/selftests/vDSO/parse_vdso.c

@@ -56,12 +56,15 @@ static struct vdso_info
 } vdso_info;
 
 /* Straight from the ELF specification. */
-static unsigned long elf_hash(const unsigned char *name)
+static unsigned long elf_hash(const char *name)
 {
 	unsigned long h = 0, g;
-	while (*name)
+	const unsigned char *s;
+
+	s = (const unsigned char *) name;
+	while (*s)
 	{
-		h = (h << 4) + *name++;
+		h = (h << 4) + *s++;
 		g = h & 0xf0000000;
 		if (h)
 			h ^= g >> 24;