efi_loader: avoid crash in OpenProtocol()

efi_loader: avoid crash in OpenProtocol()

When trying to open a protocol exclusively attached drivers have to be
removed. This removes entries in the open protocol information linked list
over which we are looping. As additionally child controllers may have been
removed the only safe thing to do is to restart the loop over the linked
list when a driver is removed.

By observing the return code of DisconnectController() we can eliminate a
loop.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>