ANDROID: KVM: arm64: Fix build with CONFIG_MODULES=n

The recently introduced support for pKVM modules has clearly lacked a
bit of testing with CONFIG_MODULES=n.

Fix the broken __pkvm_init_module() stub to make the bots happy.

Bug: 244543039
Bug: 244373730
Reported-by: kernel test robot <lkp@intel.com>
Change-Id: Ie59cbf46442721de78ef51523debadc4c156530e
Signed-off-by: Quentin Perret <qperret@google.com>