usb: storage: s/CONFIG_BLK/CONFIG_IS_ENABLED(BLK)/

This fixes link issues when building the SPL without USB driver model
but with USB storage support. CONFIG_BLK can be enabled and disabled
independently for SPL and non-SPL builds. We leverage that existing
functionality here.

Signed-off-by: Sven Schwermer <sven@svenschwermer.de>
1 file changed