As of commit e2a2e56e ("arm64: dump: no need to check return value
of debugfs_create functions") in the arm64 for-next/core branch,
ptdump_debugfs_register does not have a return value, which causes a
build error here:

drivers/firmware/efi/arm-runtime.c:51:9: error: returning 'void' from a
function with incompatible result type 'int'
        return ptdump_debugfs_register(&efi_ptdump_info, "efi_page_tables");
               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1 error generated.

The arm version is still awaiting acceptance [1] but in anticipation
of that patch being merged, restructure this function to call
ptdump_debugfs_register without expecting a return value.

[1]: https://lore.kernel.org/lkml/20190122144114.9816-3-gregkh@linuxfoundation.org/Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>