mfd: max77843: Fix max77843_chg_init() return on error

If i2c_new_dummy() fails in max77843_chg_init(), an PTR_ERR(NULL) is
returned which is 0. So the function was wrongly returning a success
value instead of an error code.

Cc: stable@vger.kernel.org # 4.1
Fixes: c7f585fe

 ("mfd: max77843: Add max77843 MFD driver core driver")
Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>
Reviewed-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>