powerpc/smp: Add check for kcalloc() failure in parse_thread_groups()

powerpc/smp: Add check for kcalloc() failure in parse_thread_groups()

As kcalloc() may fail, check its return value to avoid a NULL pointer
dereference when passing it to of_property_read_u32_array().

Fixes: 790a1662d3a26 ("powerpc/smp: Parse ibm,thread-groups with multiple properties")
Cc: stable@vger.kernel.org
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Guangshuo Li <lgs201920130244@gmail.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20250923133235.1862108-1-lgs201920130244@gmail.com