wil6210: map RGF_USER_USAGE_1 on the debugfs

Firmware sets this register with the offset of the firmware trace area
within the peripheral memory region. Critical for the firmware trace
to work

Signed-off-by: Vladimir Kondratiev <qca_vkondrat@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>