drivers: ethernet: cpsw: fix panic when interrupt coaleceing is set via ethtool

In the Linux kernel, the following vulnerability has been resolved:

drivers: ethernet: cpsw: fix panic when interrupt coaleceing is set via ethtool

cpsw_ethtool_begin directly returns the result of pm_runtime_get_sync
when successful.
pm_runtime_get_sync returns -error code on failure and 0 on successful
resume but also 1 when the device is already active. So the common case
for cpsw_ethtool_begin is to return 1. That leads to inconsistent calls
to pm_runtime_put in the call-chain so that pm_runtime_put is called
one too many times and as result leaving the cpsw dev behind suspended.

The suspended cpsw dev leads to an access violation later on by
different parts of the cpsw driver.

Fix this by calling the return-friendly pm_runtime_resume_and_get
function.