arch_topology: Fix incorrect error check in topology_parse_cpu_capacity()

arch_topology: Fix incorrect error check in topology_parse_cpu_capacity()

Fix incorrect use of PTR_ERR_OR_ZERO() in topology_parse_cpu_capacity()
which causes the code to proceed with NULL clock pointers. The current
logic uses !PTR_ERR_OR_ZERO(cpu_clk) which evaluates to true for both
valid pointers and NULL, leading to potential NULL pointer dereference
in clk_get_rate().

Per include/linux/err.h documentation, PTR_ERR_OR_ZERO(ptr) returns:
"The error code within @ptr if it is an error pointer; 0 otherwise."

This means PTR_ERR_OR_ZERO() returns 0 for both valid pointers AND NULL
pointers. Therefore !PTR_ERR_OR_ZERO(cpu_clk) evaluates to true (proceed)
when cpu_clk is either valid or NULL, causing clk_get_rate(NULL) to be
called when of_clk_get() returns NULL.

Replace with !IS_ERR_OR_NULL(cpu_clk) which only proceeds for valid
pointers, preventing potential NULL pointer dereference in clk_get_rate().

Cc: stable <stable@kernel.org>
Signed-off-by: Kaushlendra Kumar <kaushlendra.kumar@intel.com>
Reviewed-by: Sudeep Holla <sudeep.holla@arm.com>
Fixes: b8fe128dad8f ("arch_topology: Adjust initial CPU capacities with current freq")
Link: https://patch.msgid.link/20250923174308.1771906-1-kaushlendra.kumar@intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>