spi: spi-fsl-dspi: Fix imprecise abort on VF500 during probe

commit d8ffee2f551a627ffb7b216e2da322cb9a037f77 upstream.

Registers of DSPI should not be accessed before enabling its clock.  On
Toradex Colibri VF50 on Iris carrier board this could be seen during
bootup as imprecise abort:

    Unhandled fault: imprecise external abort (0x1c06) at 0x00000000
    Internal error: : 1c06 [#1] ARM
    Modules linked in:
    CPU: 0 PID: 1 Comm: swapper Not tainted 4.14.39-dirty #97
    Hardware name: Freescale Vybrid VF5xx/VF6xx (Device Tree)
    Backtrace:
    [<804166a8>] (regmap_write) from [<80466b5c>] (dspi_probe+0x1f0/0x8dc)
    [<8046696c>] (dspi_probe) from [<8040107c>] (platform_drv_probe+0x54/0xb8)
    [<80401028>] (platform_drv_probe) from [<803ff53c>] (driver_probe_device+0x280/0x2f8)
    [<803ff2bc>] (driver_probe_device) from [<803ff674>] (__driver_attach+0xc0/0xc4)
    [<803ff5b4>] (__driver_attach) from [<803fd818>] (bus_for_each_dev+0x70/0xa4)
    [<803fd7a8>] (bus_for_each_dev) from [<803fee74>] (driver_attach+0x24/0x28)
    [<803fee50>] (driver_attach) from [<803fe980>] (bus_add_driver+0x1a0/0x218)
    [<803fe7e0>] (bus_add_driver) from [<803fffe8>] (driver_register+0x80/0x100)
    [<803fff68>] (driver_register) from [<80400fdc>] (__platform_driver_register+0x48/0x50)
    [<80400f94>] (__platform_driver_register) from [<8091cf7c>] (fsl_dspi_driver_init+0x1c/0x20)
    [<8091cf60>] (fsl_dspi_driver_init) from [<8010195c>] (do_one_initcall+0x4c/0x174)
    [<80101910>] (do_one_initcall) from [<80900e8c>] (kernel_init_freeable+0x144/0x1d8)
    [<80900d48>] (kernel_init_freeable) from [<805ff6a8>] (kernel_init+0x10/0x114)
    [<805ff698>] (kernel_init) from [<80107be8>] (ret_from_fork+0x14/0x2c)

Cc: <stable@vger.kernel.org>
Fixes: 5ee67b58 ("spi: dspi: clear SPI_SR before enable interrupt")
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>