examples/bbdev: fix header include for musl

The header file unistd.h should not be included from sys/ directory,
it is an error with musl libc.

Fixes: 1ffee690eaa1 ("examples/bbdev: add sample app")
Cc: stable@dpdk.org

Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
Acked-by: Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>
Acked-by: David Marchand <david.marchand@redhat.com>

examples/bbdev_app/main.c

@@ -8,7 +8,7 @@
 #include <stdint.h>
 #include <inttypes.h>
 #include <sys/types.h>
-#include <sys/unistd.h>
+#include <unistd.h>
 #include <sys/queue.h>
 #include <stdarg.h>
 #include <ctype.h>