receive-pack::hmac_sha1(): copy the entire SHA-1 hash out

clang gives the following warning:

builtin/receive-pack.c:327:35: error: sizeof on array function
parameter will return size of 'unsigned char *' instead of 'unsigned
char [20]' [-Werror,-Wsizeof-array-argument]
        git_SHA1_Update(&ctx, out, sizeof(out));
                                         ^
builtin/receive-pack.c:292:37: note: declared here
static void hmac_sha1(unsigned char out[20],
                                   ^
Signed-off-by: Brian Gernhardt <brian@gernhardtsoftware.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/receive-pack.c

@@ -288,7 +288,7 @@ static int copy_to_sideband(int in, int out, void *arg)
 
 #define HMAC_BLOCK_SIZE 64
 
-static void hmac_sha1(unsigned char out[20],
+static void hmac_sha1(unsigned char *out,
 		      const char *key_in, size_t key_len,
 		      const char *text, size_t text_len)
 {
@@ -323,7 +323,7 @@ static void hmac_sha1(unsigned char out[20],
 	/* RFC 2104 2. (6) & (7) */
 	git_SHA1_Init(&ctx);
 	git_SHA1_Update(&ctx, k_opad, sizeof(k_opad));
-	git_SHA1_Update(&ctx, out, sizeof(out));
+	git_SHA1_Update(&ctx, out, 20);
 	git_SHA1_Final(out, &ctx);
 }