iwlwifi: mvm: remove newline from rs_pretty_print_rate()

Some of the places using this want the newline, but not all,
so remove the newline from it and generate it in the debugfs
files where it's desired.

The effect of this is not printing double newlines in debug
log messages.

Change-Id: Ia59b0abbef16b6783fcabc095c5fde16bd047a26
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>