net: ipa: don't return a value from gsi_channel_command()

Callers of gsi_channel_command() no longer care whether the command
times out, and don't use what gsi_channel_command() returns.  Redefine
that function to have void return type.

Reported-by: kernel test robot <lkp@intel.com>
Fixes: 6ffddf3b ("net: ipa: use state to determine channel command success")
Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>