mfd: vexpress: Add parentheses around bridge->ops->regmap_init call

regmap_init(...) is a macro since commit
"regmap: Use different lockdep class for each regmap init call".
That same name is used as a function pointer: prevent its expansion
by adding parentheses around the function pointer.

Signed-off-by: Nicolas Boichat <drinkcat@chromium.org>
Signed-off-by: Mark Brown <broonie@kernel.org>