spi/bcm63xx: Move default clock configuration to kill compiler warning

drivers/spi/spi-bcm63xx.c: In function ‘bcm63xx_spi_setup_transfer’:
drivers/spi/spi-bcm63xx.c:207: warning: ‘clk_cfg’ may be used uninitialized in this function

While this is a false positive, it can easily be avoided by selecting
the default clock configuration first.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Mark Brown <broonie@kernel.org>