mei: bus: suppress sign-compare warnings

mei: bus: suppress sign-compare warnings

Comparison between signed and unsigned warnings
and associated type promotion may cause error
condition not be detected.
The type promotion issue in mei bus was addressed by two patches:
commit 81122f04b9e0 ("mei: bus: type promotion bug in mei_nfc_if_version()")
commit 071754daceec ("mei: bus: type promotion bug in mei_fwver()")
Now it is possible to suppress the warning, by adding proper
casting to move out of radar.

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>