serial: msm_geni_serial: Reset UART error code to default during shutdown

Currently driver is seting UART error code to default only when
BT host calling TIOCFAULT crash ioctl.

This change is to reset UART error code to default during shutdown
so that it will helps in passing correct UART error code from UART driver
from next session.

Change-Id: I2a073634699d54e905ca3970392563f7d8130640
Signed-off-by: Chandana Kishori Chiluveru <cchiluve@codeaurora.org>