i2c: nvidia-gpu: refactor master_xfer

Added a local variable "send_stop" to simplify "goto" statements.

The "send_stop" handles below two case
1) When first i2c start fails and so i2c stop is not sent before
exiting

2) When i2c stop failed after all transfers and we do not need to
send another stop before exiting.

Signed-off-by: Ajay Gupta <ajayg@nvidia.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>