ARM SCMI fixes for v5.14

A small set of fixes:
- adding check for presence of probe while registering the driver to
  prevent NULL pointer access
- dropping the duplicate check as the driver core already takes care of it
- fix for possible scmi_linux_errmap buffer overflow
- fix to avoid sensor message structure padding
- fix the range check for the maximum number of pending SCMI messages
- fix for various kernel-doc warnings

* tag 'scmi-fixes-5.14' of git://git.kernel.org/pub/scm/linux/kernel/git/sudeep.holla/linux:
  firmware: arm_scmi: Fix range check for the maximum number of pending messages
  firmware: arm_scmi: Avoid padding in sensor message structure
  firmware: arm_scmi: Fix kernel doc warnings about return values
  firmware: arm_scpi: Fix kernel doc warnings
  firmware: arm_scmi: Fix kernel doc warnings
  firmware: arm_scmi: Fix possible scmi_linux_errmap buffer overflow
  firmware: arm_scmi: Ensure drivers provide a probe function
  firmware: arm_scmi: Simplify device probe function on the bus

Link: https://lore.kernel.org/r/20210714165831.2617437-1-sudeep.holla@arm.com
Signed-off-by: Arnd Bergmann <arnd@arndb.de>