mci/stm378x warning

[Jean-Christophe PLAGNIOL-VILLARD]

HI,

	durring some night build I see this on the drivers/mci/stm378x.c

	/opt/work/barebox/drivers/mci/stm378x.c: In function 'mci_request':
	/opt/work/barebox/drivers/mci/stm378x.c:354: warning: 'length' may be used uninitialized in this function
	/opt/work/barebox/drivers/mci/stm378x.c:354: note: 'length' was declared here

	so I guess length will initialized at 0

Best Regards,
J.