drm/radeon/ni: Fix wrong firmware size logging in ni_init_microcode()

Clean up a typo in pr_err() erroneously printing NI MC 'rdev->mc_fw->size'
during SMC firmware load. Log 'rdev->smc_fw->size' instead.

Found by Linux Verification Center (linuxtesting.org) with static
analysis tool SVACE.

Fixes: 6596afd4

 ("drm/radeon/kms: add dpm support for btc (v3)")
Signed-off-by: Nikita Zhandarovich <n.zhandarovich@fintech.ru>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>