mmc: pwrseq: Use bitmap_free() to free bitmap

kfree() and bitmap_free() are the same. But using the later is more
consistent when freeing memory allocated with bitmap_alloc().

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/07a8e48db446888bd77f16b88568e80904f52103.1640528089.git.christophe.jaillet@wanadoo.fr


Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>