Use driver name as the log prefix in standard functions

Use driver name as the log prefix in standard functions

Some of the standard helper functions take a log prefix parameter that is
used when printing messages. This log prefix is almost always identical to
the name field in the driver's sr_dev_driver struct. The only exception are
drivers which register multiple sr_dev_driver structs.

Instead of passing the log prefix as a parameter simply use the driver's
name. This simplifies the API, gives consistent behaviour between different
drivers and also makes it easier to identify where the message originates
when a driver registers sr_dev_driver structs.

Signed-off-by: Lars-Peter Clausen <redacted>