powerpc: mpc85xx: Fix incorrect application of patch

I messed up application of patch 5a428e75 ("mmc: fsl_esdhc_spl: Add
support for builds without CONFIG_SYS_MMC_U_BOOT_OFFS"). I took it from
a work-in-progress branch where I changed usage of
  CONFIG_SDCARD to CONFIG_SD_BOOT
and refactored
  SYS_MPC85XX_NO_RESETVEC
mess.

But these changes aren't in master yet. Fix the wrong usage of these
macros.

Fixes: 5a428e75 ("mmc: fsl_esdhc_spl: Add support for builds without
CONFIG_SYS_MMC_U_BOOT_OFFS")
Signed-off-by: Marek Behún <kabel@kernel.org>
Reviewed-by: Pali Rohár <pali@kernel.org>