staging: rtlwifi: remove redundant initialization of 'cfg_cmd'

The initialization of cfg_cmd is redundant as the value is never read
and it is being re-assigned to cfg_cmd = pwrcfgcmd[ary_idx] inside a
loop, hence it can be removed.

Cleans up clang warning:
drivers/staging/rtlwifi/core.c:1819:22: warning: Value stored to
'cfg_cmd' during its initialization is never read

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>