iwlwifi: mvm: fix the return type for DSM functions 1 and 2

The return type value of functions 1 and 2 were considered to be an
integer inside a buffer, but they can also be only an integer, without
the buffer.  Fix the code in iwl_acpi_get_dsm_u8() to handle it as a
single integer value, as well as packed inside a buffer.

Signed-off-by: Matt Chen <matt.chen@intel.com>
Fixes: 9db93491 ("iwlwifi: acpi: support device specific method (DSM)")
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/iwlwifi.20210122144849.5757092adcd6.Ic24524627b899c9a01af38107a62a626bdf5ae3a@changeid