sunxi: SPI: fix pinmuxing for Allwinner H6 SoCs

sunxi: SPI: fix pinmuxing for Allwinner H6 SoCs

The driver for SPI0 on Allwinner H6 SoCs did not use the correct define
SUN50I_GPC_SPI0 for the pin function, but one for a different Allwinner
SoC series.

Fix the conditionals to use the correct define for H6 SoCs. This matches
the conditional logic in the SPL spi driver.

Tested by probing the spi-flash on a pine64_h64-model-b board with
adapted device-tree (disable mmc2, enable spi0).

Signed-off-by: Daniel Wagenknecht <dwagenk@mailbox.org>
Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Andre Przywara <andre.przywara@arm.com>