Input: synaptics-rmi4 - fix command completion check for bootloader v7/v8

Input: synaptics-rmi4 - fix command completion check for bootloader v7/v8

The command register is reset to 0 when a command has completed. Check
for this condition instead of the error status, which will not accurately
reflect completion. In particular, the incorrect condition caused every
command error to be reported as a timeout.

Signed-off-by: Matthias Schiffer <matthias.schiffer@ew.tq-group.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Link: https://lore.kernel.org/r/20220608124808.51402-4-matthias.schiffer@ew.tq-group.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>