coresight:dbgui: Use unsigned long pointer var for 3rd arg of kstrtoul

Type-casting pointer from uint32_t to unsigned long is resulting in
a fault while doing conversion in kstrtoul.

Use a separate variable of type 'unsigned long' to avoid fault
during conversion.

Change-Id: Idbb9505cb9bc621134f23e944d464b0ee1d777f7
CRs-Fixed: 2194067
Signed-off-by: Mukesh Ojha <mojha@codeaurora.org>