uart_qmsi: Remove uart_qmsi_pm_save_config

One remaining reference to uart_qmsi_pm_save_config
was missed by patch bc60506d.

This reference is removed.

This fixes the following error:
...
drivers/built-in.o: In function `uart_qmsi_line_ctrl_set':
/drivers/serial/uart_qmsi.c:439:
undefined reference to `uart_qmsi_pm_save_config'
collect2: error: ld returned 1 exit status
...

Change-Id: I1ceda0e152db5a1c7f70d67c04b931416687031a
Signed-off-by: Julien Delayen <julien.delayen@intel.com>