textfile: Fix a pointer arithmetic logic bug in read_key()
textfile: Fix a pointer arithmetic logic bug in read_key()

A substraction of pointers ends up in a wrong computation of the size
passed to strnpbrk() in read_key(). This patch fixes the pointer logic.

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