i2c: nvidia-gpu: drop empty stub for runtime pm

After the commit c5eb1190 ("PCI / PM: Allow runtime PM without callback
functions") we no more need empty stubs for runtime-pm to work.

The driver has no device specific task(s) for .suspend() . The stub was
placed just for runtime-pm, which can be dropped now.

Reported-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Vaibhav Gupta <vaibhavgupta40@gmail.com>
Reviewed-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>