mfd: ssbi: Use devm_* and simplify code

Use devm_ioremap_resource and devm_kzalloc to simplify error
paths and reduce lines of code. Also use dev_err() to keep
consistency and drop the .remove function because the devm
functions take care of what it's doing besides the now obsolete
platform_set_drvdata() which we can just drop. Finally, use
module_platform_driver() to save some more lines.

Cc: David Brown <davidb@codeaurora.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: David Brown <davidb@codeaurora.org>