pmic: tps65090: correct checking i2c bus

The function tps65090_init checks the i2c bus of p->bus. However
the pointer p is not intialiased at this point. Check the local
variable bus instead.

cc: Tom Wai-Hong Tam <waihong@chromium.org>
Signed-off-by: Jeroen Hofstee <jeroen@myspectrum.nl>
Acked-by: Simon Glass <sjg@chromium.org>