usb: dwc3: core: do not queue work if dr_mode is not USB_DR_MODE_OTG

usb: dwc3: core: do not queue work if dr_mode is not USB_DR_MODE_OTG

Do not try to queue a drd work if dr_mode is not USB_DR_MODE_OTG
because the work is not inited, this may be triggered by user try
to change mode file of debugfs on a single role port, which will
cause below kernel dump:
[   60.115529] ------------[ cut here ]------------
[   60.120166] WARNING: CPU: 1 PID: 627 at kernel/workqueue.c:1473
__queue_work+0x46c/0x520
[   60.128254] Modules linked in:
[   60.131313] CPU: 1 PID: 627 Comm: sh Not tainted
5.7.0-rc4-00022-g914a586-dirty #135
[   60.139054] Hardware name: NXP i.MX8MQ EVK (DT)
[   60.143585] pstate: a0000085 (NzCv daIf -PAN -UAO)
[   60.148376] pc : __queue_work+0x46c/0x520
[   60.152385] lr : __queue_work+0x314/0x520
[   60.156393] sp : ffff8000124ebc40
[   60.159705] x29: ffff8000124ebc40 x28: ffff800011808018
[   60.165018] x27: ffff800011819ef8 x26: ffff800011d39980
[   60.170331] x25: ffff800011808018 x24: 0000000000000100
[   60.175643] x23: 0000000000000013 x22: 0000000000000001
[   60.180955] x21: ffff0000b7c08e00 x20: ffff0000b6c31080
[   60.186267] x19: ffff0000bb99bc00 x18: 0000000000000000
[   60.191579] x17: 0000000000000000 x16: 0000000000000000
[   60.196891] x15: 0000000000000000 x14: 0000000000000000
[   60.202202] x13: 0000000000000000 x12: 0000000000000000
[   60.207515] x11: 0000000000000000 x10: 0000000000000040
[   60.212827] x9 : ffff800011d55460 x8 : ffff800011d55458
[   60.218138] x7 : ffff0000b7800028 x6 : 0000000000000000
[   60.223450] x5 : ffff0000b7800000 x4 : 0000000000000000
[   60.228762] x3 : ffff0000bb997cc0 x2 : 0000000000000001
[   60.234074] x1 : 0000000000000000 x0 : ffff0000b6c31088
[   60.239386] Call trace:
[   60.241834]  __queue_work+0x46c/0x520
[   60.245496]  queue_work_on+0x6c/0x90
[   60.249075]  dwc3_set_mode+0x48/0x58
[   60.252651]  dwc3_mode_write+0xf8/0x150
[   60.256489]  full_proxy_write+0x5c/0xa8
[   60.260327]  __vfs_write+0x18/0x40
[   60.263729]  vfs_write+0xdc/0x1c8
[   60.267045]  ksys_write+0x68/0xf0
[   60.270360]  __arm64_sys_write+0x18/0x20
[   60.274286]  el0_svc_common.constprop.0+0x68/0x160
[   60.279077]  do_el0_svc+0x20/0x80
[   60.282394]  el0_sync_handler+0x10c/0x178
[   60.286403]  el0_sync+0x140/0x180
[   60.289716] ---[ end trace 70b155582e2b7988 ]---

Signed-off-by: Li Jun <jun.li@nxp.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>