mmc: Use regulator_set_enable_if_allowed

mmc: Use regulator_set_enable_if_allowed

With the commit 4fcba5d556b4 ("regulator: implement basic reference
counter") the return value of regulator_set_enable may be EALREADY or
EBUSY for fixed/gpio regulators.

Change to use the more relaxed regulator_set_enable_if_allowed to
continue if regulator already was enabled or disabled.

Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Tested-by: Svyatoslav Ryhel <clamor95@gmail.com> # P895 Tegra 3;
Reviewed-by: Simon Glass <sjg@chromium.org>
Tested-by: Simon Glass <sjg@chromium.org>  # rockpro64-rk3399
[backport of the commit d3de38554a35e96872e43644b683e32f018c46a8 from mainline]
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Change-Id: I3cb6dc82d7dbc54103266af5960b807e4af1692c