iwlwifi: mvm: check return value of rs_rate_from_ucode_rate()

iwlwifi: mvm: check return value of rs_rate_from_ucode_rate()

The rs_rate_from_ucode_rate() function may return -EINVAL if the rate
is invalid, but none of the callsites check for the error, potentially
making us access arrays with index IWL_RATE_INVALID, which is larger
than the arrays, causing an out-of-bounds access.  This will trigger
KASAN warnings, such as the one reported in the bugzilla issue
mentioned below.

This fixes https://bugzilla.kernel.org/show_bug.cgi?id=200659

Cc: stable@vger.kernel.org
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>