Currently there is no btrfs support in SPL. But macro CONFIG_FS_BTRFS is defined also when building SPL. When both FS_BTRFS and SPL are enabled then build process throw compile error. Fix check for btrfs code in fstypes[] to allow compiling FS_BTRFS only in proper U-Boot. Signed-off-by: Pali Rohár <pali@kernel.org>