ubi: enable error reporting in initialization

The UBI layer will disable much of its error reporting when it is
compiled into the linux kernel to avoid stopping boot.  We want this
error reporting in U-Boot since we don't initialize the UBI layer until
it is used and want the error reporting.

We force this by telling the UBI layer we are building as a module.

Signed-off-by: Andrew Ruder <andrew.ruder@elecsyscorp.com>
Cc: Wolfgang Denk <wd@denx.de>
Cc: Heiko Schocher <hs@denx.de>
Cc: Kyungmin Park <kmpark@infradead.org>