msm: lpm-levels-of: avoid NULL pointer dereference

Cpu node name is printed in error case when its matching
node is not found. If cpu_node is NULL we must avoid its
dereference. Move the print statement so that it is not
accessed when cpu node variable is NULL.

Change-Id: I373d668403c61e9fce76d1d5b4d0f225fa277d16
Signed-off-by: Venkat Devarasetty <vdevaras@codeaurora.org>