hwspinlock: omap: Change to use devm_platform_ioremap_resource()

Use the new helper that wraps the calls to platform_get_resource()
and devm_ioremap_resource() together, which can simpify the code.
Meanwhile renaming the error label to make more sense after removing
iounmap().

Signed-off-by: Baolin Wang <baolin.wang7@gmail.com>
Link: https://lore.kernel.org/r/6c09c5034a7e68fdfc22d2cb5daa375bccb33a66.1578453062.git.baolin.wang7@gmail.com


Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>