drm/msm/mdp5: Fix global state lock backoff

In the Linux kernel, the following vulnerability has been resolved:

drm/msm/mdp5: Fix global state lock backoff

We need to grab the lock after the early return for !hwpipe case.

Otherwise, we could have hit contention yet still returned 0.

Fixes an issue that the new CONFIG_DRM_DEBUG_MODESET_LOCK stuff flagged

in CI:

WARNING: CPU: 0 PID: 282 at drivers/gpu/drm/drm_modeset_lock.c:296 drm_modeset_lock+0xf8/0x154

Modules linked in:

CPU: 0 PID: 282 Comm: kms_cursor_lega Tainted: G W 5.19.0-rc2-15930-g875cc8bc536a #1

Hardware name: Qualcomm Technologies, Inc. DB820c (DT)

pstate: 60000005 (nZCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)

pc : drm_modeset_lock+0xf8/0x154

lr : drm_atomic_get_private_obj_state+0x84/0x170

sp : ffff80000cfab6a0

x29: ffff80000cfab6a0 x28: 0000000000000000 x27: ffff000083bc4d00

x26: 0000000000000038 x25: 0000000000000000 x24: ffff80000957ca58

x23: 0000000000000000 x22: ffff000081ace080 x21: 0000000000000001

x20: ffff000081acec18 x19: ffff80000cfabb80 x18: 0000000000000038

x17: 0000000000000000 x16: 0000000000000000 x15: fffffffffffea0d0

x14: 0000000000000000 x13: 284e4f5f4e524157 x12: 5f534b434f4c5f47

x11: ffff80000a386aa8 x10: 0000000000000029 x9 : ffff80000cfab610

x8 : 0000000000000029 x7 : 0000000000000014 x6 : 0000000000000000

x5 : 0000000000000001 x4 : ffff8000081ad904 x3 : 0000000000000029

x2 : ffff0000801db4c0 x1 : ffff80000cfabb80 x0 : ffff000081aceb58

Call trace:

drm_modeset_lock+0xf8/0x154

drm_atomic_get_private_obj_state+0x84/0x170

mdp5_get_global_state+0x54/0x6c

mdp5_pipe_release+0x2c/0xd4

mdp5_plane_atomic_check+0x2ec/0x414

drm_atomic_helper_check_planes+0xd8/0x210

drm_atomic_helper_check+0x54/0xb0

...

---[ end trace 0000000000000000 ]---

drm_modeset_lock attempting to lock a contended lock without backoff:

drm_modeset_lock+0x148/0x154

mdp5_get_global_state+0x30/0x6c

mdp5_pipe_release+0x2c/0xd4

mdp5_plane_atomic_check+0x290/0x414

drm_atomic_helper_check_planes+0xd8/0x210

drm_atomic_helper_check+0x54/0xb0

drm_atomic_check_only+0x4b0/0x8f4

drm_atomic_commit+0x68/0xe0

Patchwork: https://patchwork.freedesktop.org/patch/492701/