can: mcp251x: Call wrapper instead of regulator_disable()

There is no need to check for regulator presence in the ->suspend()
since a wrapper does it for us. Due to this we may unconditionally set
AFTER_SUSPEND_POWER flag.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>