fadvise64_64() has two 64-bit arguments at the wrong alignment
for hexagon, which turns them into a 7-argument syscall that is
not supported by Linux.

The downstream musl port for hexagon actually asks for a 6-argument
version the same way we do it on arm, csky, powerpc, so make the
kernel do it the same way to avoid having to change both.

Link: https://github.com/quic/musl/blob/hexagon/arch/hexagon/syscall_arch.h#L78
Cc: stable@vger.kernel.org
Signed-off-by: Arnd Bergmann <arnd@arndb.de>