platform/x86: intel_pmc_core: Uninitialized data in pmc_core_lpm_latch_mode_write()

platform/x86: intel_pmc_core: Uninitialized data in pmc_core_lpm_latch_mode_write()

The simple_write_to_buffer() can return success if even a single byte
is copied from user space.  In this case it can result in using
uninitalized data if the buf[] array is not fully initialized.  Really
we should only succeed if the whole buffer is copied.

Just using copy_from_user() is simpler and more appropriate.

Fixes: 8074a79fad2e ("platform/x86: intel_pmc_core: Add option to set/clear LPM mode")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Link: https://lore.kernel.org/r/YIBCf+G9Ef8wrGJw@mwanda
Signed-off-by: Hans de Goede <hdegoede@redhat.com>