uio: uio_sercos3: use device-managed functions for simple allocs

uio: uio_sercos3: use device-managed functions for simple allocs

This change converts the simple allocations [kzalloc()] to devm_kzalloc()
tying the life-time of these objects to the PCI device object.
It cleans up the error and exit path and bit, and does a minor correction
that -ENOMEM is returned (vs -ENODEV) in case the 'priv' object cannot be
allocated.

Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Link: https://lore.kernel.org/r/20201120084207.50736-1-alexandru.ardelean@analog.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>