hciattach: make set_speed return error if any operation fails
hciattach: make set_speed return error if any operation fails

This patch lets set_speed function changing UART baud rate to return an
error code if any one operation fails instead of returning only the last
operation's status.

mapfau/bluez,pstglia/external-bluetooth-bluez,ComputeCycles/bluez,silent-snowman/bluez,mapfau/bluez,mapfau/bluez,mapfau/bluez,silent-snowman/bluez,pkarasev3/bluez,pkarasev3/bluez,pstglia/external-bluetooth-bluez,ComputeCycles/bluez,silent-snowman/bluez,ComputeCycles/bluez,ComputeCycles/bluez,pkarasev3/bluez,pstglia/external-bluetooth-bluez,pkarasev3/bluez,silent-snowman/bluez,pstglia/external-bluetooth-bluez