mmc: sdhci-of-bst: Fix memory leak in sdhci_bst_alloc_bounce_buffer()

mmc: sdhci-of-bst: Fix memory leak in sdhci_bst_alloc_bounce_buffer()

In sdhci_bst_alloc_bounce_buffer(), if dma_alloc_coherent() fails, the
function immediately returns -ENOMEM without releasing the reserved
memory, which results in a memory leak.

Add the missing of_reserved_mem_device_release() call before returning
-ENOMEM to properly clean up the reserved memory.

Fixes: 695824f45629 ("mmc: sdhci: add Black Sesame Technologies BST C1200 controller driver")
Signed-off-by: Felix Gu <ustc.gu@gmail.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>