Commit c6b90653 ("drivers/perf: arm_pmu: make info messages more
verbose") breaks booting on systems where the PMU is probed without
devicetree (e.g by inspecting the MIDR of the current CPU). In this case,
pdev->dev.of_node is NULL and we shouldn't try to access its ->fullname
field when printing probe error messages.

This patch fixes the probing code to use of_node_full_name, which safely
handles NULL nodes and removes the "Error %i" part of the string, since
it's not terribly useful.
Reported-by: NGuenter Roeck <private@roeck-us.net>
Signed-off-by: NWill Deacon <will.deacon@arm.com>