drivers/bluetooth: btbcm: Use kmalloc_array() to prevent overflow

drivers/bluetooth: btbcm: Use kmalloc_array() to prevent overflow

Replace the open-coded multiplication in kmalloc() with a call
to kmalloc_array() to prevent potential integer overflows.

This is a mechanical change, replacing BCM_FW_NAME_LEN with
the type-safe sizeof(*fw_name) as the element size

Signed-off-by: Ayaan Mirza Baig <ayaanmirzabaig85@gmail.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>