package/qemu: disable libssh for the host variant

package/qemu: disable libssh for the host variant

There is no host-libssh in Buildroot, avoid qemu build system
to find libssh from the host.

Under certain circumstances (host distribution, openssl version), the
qemu-system binary fail to start:

host/bin/qemu-system-aarch64: symbol lookup error: /lib64/libssh.so.4: undefined symbol: EVP_KDF_ctrl, version OPENSSL_1_1_1b

$ ldd output/host/bin/qemu-system-aarch64
	[...]
	libssh.so.4 => /lib64/libssh.so.4

Explicitely disable libssh for the host variant.

Signed-off-by: Romain Naour <romain.naour@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>