regulator: max8907: fix compile error when !CONFIG_OF

Fix the following:

  CC [M]  drivers/regulator/max8907-regulator.o
drivers/regulator/max8907-regulator.c: In function 'max8907_regulator_probe':
drivers/regulator/max8907-regulator.c:297:12: error: 'max8907_matches' undeclared (first use in this function)

by removing direct references to max8907_matches[], which only exists when
CONFIG_OF is defined.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>