In the case where size is zero the while loop never assigns rc and the
return value is uninitialized. Fix this by initializing rc to zero.

Fixes: 639781dc ("habanalabs/gaudi: add debugfs to DMA from the device")
Reviewed-by: NOded Gabbay <ogabbay@kernel.org>
Acked-by: NArnd Bergmann <arnd@arndb.de>
Signed-off-by: NColin Ian King <colin.king@canonical.com>
Addresses-Coverity: ("Uninitialized scalar variable")
Link: https://lore.kernel.org/r/20210412161012.1628202-1-colin.king@canonical.comSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>