regulator: core: fix documentation error in regulator_allow_bypass

commit f59c8f9f (regulator: core: Support bypass mode)
has a short documentation error around the regulator_allow_bypass
parameter 'enable' which is documented as 'allow'.

This generates kernel-doc warning as follows:
./scripts/kernel-doc drivers/regulator/core.c >/dev/null
Warning(drivers/regulator/core.c:2841): No description found for parameter 'enable'
Warning(drivers/regulator/core.c:2841): Excess function parameter 'allow' description in 'regulator_allow_bypass'

Cc: Liam Girdwood <lgirdwood@gmail.com>
Cc: Mark Brown <broonie@opensource.wolfsonmicro.com>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>