If the dwc2 driver fails to probe after having enabled the regulators,
it ends up being unregistered with regulators enabled, something the
core regulator code is legitimately upset about:

   dwc2 ff400000.usb: supply vusb_d not found, using dummy regulator
   dwc2 ff400000.usb: supply vusb_a not found, using dummy regulator
   dwc2 ff400000.usb: dwc2_core_reset: HANG! AHB Idle timeout GRSTCTL GRSTCTL_AHBIDLE
   WARNING: CPU: 2 PID: 112 at drivers/regulator/core.c:2074 _regulator_put.part.0+0x16c/0x174
   Modules linked in: dwc2(E+) dwc3(E) udc_core(E) rtc_hym8563(E) dwmac_generic(E) ulpi(E) usbcore(E) dwc3_meson_g12a(E) roles(E) meson_gx_mmc(E+) i2c_meson(E) mdio_mux_meson_g12a(E) mdio_mux(E) dwmac_meson8b(E) stmmac_platform(E) stmmac(E) mdio_xpcs(E) phylink(E) of_mdio(E) fixed_phy(E) libphy(E) pwm_regulator(E) fixed(E)
   CPU: 2 PID: 112 Comm: systemd-udevd Tainted: G            E     5.9.0-rc4-00102-g423583bc8cf9 #1840
   Hardware name: amlogic w400/w400, BIOS 2020.04 05/22/2020
   pstate: 80400009 (Nzcv daif +PAN -UAO BTYPE=--)
   pc : _regulator_put.part.0+0x16c/0x174
   lr : regulator_bulk_free+0x6c/0x9c
   sp : ffffffc012353820
   x29: ffffffc012353820 x28: ffffff805a4b7000
   x27: ffffff8059c2eac0 x26: ffffff8059c2e810
   x25: ffffff805a4b7d00 x24: ffffffc008cf3028
   x23: ffffffc011729ef8 x22: ffffff807e2761d8
   x21: ffffffc01171df78 x20: ffffff805a4b7700
   x19: ffffff805a4b7700 x18: 0000000000000030
   x17: 0000000000000000 x16: 0000000000000000
   x15: ffffff807ea8d178 x14: 3935312820435455
   x13: 2038323a36313a37 x12: ffffffffffffffff
   x11: 0000000000000040 x10: 0000000000000007
   x9 : ffffffc0106f77d0 x8 : ffffffffffffffe0
   x7 : ffffffffffffffff x6 : 0000000000017702
   x5 : ffffff805a4b7400 x4 : 0000000000000000
   x3 : ffffffc01171df78 x2 : ffffff807ea8cc40
   x1 : 0000000000000000 x0 : 0000000000000001
   Call trace:
    _regulator_put.part.0+0x16c/0x174
    regulator_bulk_free+0x6c/0x9c
    devm_regulator_bulk_release+0x28/0x3c
    release_nodes+0x1c8/0x2c0
    devres_release_all+0x44/0x6c
    really_probe+0x1ec/0x504
    driver_probe_device+0x100/0x170
    device_driver_attach+0xcc/0xd4
    __driver_attach+0xb0/0x17c
    bus_for_each_dev+0x7c/0xd4
    driver_attach+0x30/0x3c
    bus_add_driver+0x154/0x250
    driver_register+0x84/0x140
    __platform_driver_register+0x54/0x60
    dwc2_platform_driver_init+0x2c/0x1000 [dwc2]
    do_one_initcall+0x54/0x2d0
    do_init_module+0x68/0x29c

In order to fix this, tie the regulator disabling to the teardown
process by registering a devm action callback. This makes sure that
the regulators are disabled at the right time (just before they are
released).

Cc: Minas Harutyunyan <hminas@synopsys.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20200914130634.2424496-1-maz@kernel.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>