shared/hfp: Fix not processing input from hfp_gw_send_error
shared/hfp: Fix not processing input from hfp_gw_send_error

If for some reason there is more than one AT command in the ring
buffer we should make sure that after upper layer sends error, AT
parser gets back to reading data from ring buffer.

Same is already done in hfp_gw_send_result() and we should handle
this in error response as well.

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