mmc: invalidate block cache after hwpart switched successfully

mmc: invalidate block cache after hwpart switched successfully

eMMC device has multiple hw partitions both address from zero. However the
mmc driver lacks block cache invalidation for switch hwpart. This causes a
problem that data of current hw partition is cached before switching to
another hw partition. And the following read operation of the latter hw
partition will get wrong data when reading from the addresses that have
been cached previously.

To solve this problem, invalidate block cache after a successful
mmc_switch_part() operation.

Signed-off-by: Weijie Gao <weijie.gao@mediatek.com>
Tested-by: Felix Brack <fb@ltec.ch>