i2c: xiic: improve error message when transfer fails to start

xiic_start_xfer can fail for different reasons:

- EBUSY: bus is busy or i2c messages still in tx_msg or rx_msg
- ETIMEDOUT: timed-out trying to clear the RX fifo
- EINVAL: wrong clock settings

Both EINVAL and ETIMEDOUT will currently print a specific error
message followed by a generic one, for example:

    Failed to clear rx fifo
    Error xiic_start_xfer

however EBUSY will simply output the generic message:

    Error xiic_start_xfer

which is not really helpful.

This commit adds a new error message when a busy condition is detected
and also removes the generic message since it does not provide any
relevant information to the user.

Signed-off-by: Marc Ferland <marc.ferland@sonatest.com>
Acked-by: Michal Simek <michal.simek@amd.com>
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>