ipmi_si: fix -Wvoid-pointer-to-enum-cast warning

ipmi_si: fix -Wvoid-pointer-to-enum-cast warning

With W=1 we see the following warning:

|  drivers/char/ipmi/ipmi_si_platform.c:272:15: error: \
|       cast to smaller integer type 'enum si_type' from \
|       'const void *' [-Werror,-Wvoid-pointer-to-enum-cast]
|    272 |         io.si_type      = (enum si_type) match->data;
|        |                           ^~~~~~~~~~~~~~~~~~~~~~~~~~

This is due to the fact that the `si_type` enum members are int-width
and a cast from pointer-width down to int will cause truncation and
possible data loss. Although in this case `si_type` has only a few
enumerated fields and thus there is likely no data loss occurring.
Nonetheless, this patch is necessary to the goal of promoting this
warning out of W=1.

Link: https://github.com/ClangBuiltLinux/linux/issues/1902
Link: https://lore.kernel.org/llvm/202308081000.tTL1ElTr-lkp@intel.com/
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Justin Stitt <justinstitt@google.com>
Message-Id: <20230809-cbl-1902-v1-1-92def12d1dea@google.com>
Signed-off-by: Corey Minyard <minyard@acm.org>