staging: btmtk_usb: use GFP_KERNEL inplace of GFP_ATOMIC in _probe path

the _probe function doesn't run in interrupt context, so no need to use
the GFP_ATOMIC allocations, instead driver can request for GFP_KERNEL

Signed-off-by: Devendra Naga <devendra.aaru@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>