Bluetooth: btmrvl_main: Replace GFP_ATOMIC with GFP_KERNEL in btmrvl_send_sync_cmd

After checking all possible call chains to btmrvl_send_sync_cmd(),
my tool finds that this function is never called in atomic context,
namely never in an interrupt handler or holding a spinlock.
And it calls wait_event_interruptible_timeout() after bt_skb_alloc(),
so it indicates that btmrvl_send_sync_cmd()
can call function which can sleep.
Thus GFP_ATOMIC is not necessary, and it can be replaced with GFP_KERNEL.

This is found by a static analysis tool named DCNS written by myself.

Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>