wifi: iwlwifi: mvm: don't try to talk to a dead firmware

In the Linux kernel, the following vulnerability has been resolved:

wifi: iwlwifi: mvm: don't try to talk to a dead firmware

This fixes:

bad state = 0

WARNING: CPU: 10 PID: 702 at drivers/net/wireless/inel/iwlwifi/iwl-trans.c:178 iwl_trans_send_cmd+0xba/0xe0 [iwlwifi]

Call Trace:

<TASK>

? __warn+0xca/0x1c0

? iwl_trans_send_cmd+0xba/0xe0 [iwlwifi 64fa9ad799a0e0d2ba53d4af93a53ad9a531f8d4]

iwl_fw_dbg_clear_monitor_buf+0xd7/0x110 [iwlwifi 64fa9ad799a0e0d2ba53d4af93a53ad9a531f8d4]

_iwl_dbgfs_fw_dbg_clear_write+0xe2/0x120 [iwlmvm 0e8adb18cea92d2c341766bcc10b18699290068a]

Ask whether the firmware is alive before sending a command.