irqchip/stm32-exti: Remove check on always false condition

The field drv_data is assigned during driver's probe, where it's
already checked to be not NULL.

Remove the always false check '!host_data->drv_data'.

This fixes a warning "variable dereferenced before check" detected
by '0-DAY CI Kernel Test Service'.

Fixes: c2974933 ("irqchip/stm32-exti: Simplify irq description table")
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Link: https://lore.kernel.org/lkml/202208131739.gJvcs9ls-lkp@intel.com/


Signed-off-by: Antonio Borneo <antonio.borneo@foss.st.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220817125758.5975-1-antonio.borneo@foss.st.com