hwspinlock: omap: Use devm_kzalloc() to allocate memory

Use devm_kzalloc() to allocate memory, which can simplify the error
handling.

Signed-off-by: Baolin Wang <baolin.wang7@gmail.com>
Link: https://lore.kernel.org/r/c066ad704c1a5fd52c3002cac80ddd59b3901b01.1578453062.git.baolin.wang7@gmail.com


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