Input: ads7846 - fix compiler warning in ads7846_probe()

This patch fixes the follwing warning introduced by commit
067fb2f6

 ("Input: ads7846 - return error on
regulator_get() failure"):

drivers/input/touchscreen/ads7846.c: In function 'ads7846_probe':
drivers/input/touchscreen/ads7846.c:1167: warning: format '%ld' expects
type 'long int', but argument 4 has type 'int'

Signed-off-by: Dmitry Torokhov <dtor@mail.ru>