tar,smemcap: silence compiler warning

gcc 11.2.1 complains that the tar header checksum might overflow
the checksum field.  It won't and using an unsigned int for the
calculation seems to convince the compiler too.

Signed-off-by: Ron Yorston <rmy@pobox.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

archival/chksum_and_xwrite_tar_header.c

@@ -15,7 +15,7 @@ void FAST_FUNC chksum_and_xwrite_tar_header(int fd, struct tar_header_t *hp)
 	 * (Sun and HP-UX gets it wrong... more details in
 	 * GNU tar source) */
 	const unsigned char *cp;
-	int chksum, size;
+	unsigned int chksum, size;
 
 	strcpy(hp->magic, "ustar  ");