rtw88: remove redundant null pointer check on arrays

The checks to see if swing_table->n or swing_table->p are null are
redundant since n and p are arrays and can never be null if
swing_table is non-null.  I believe these are redundant checks
and can be safely removed, especially the checks implies that these
are not arrays which can lead to confusion.

Addresses-Coverity: ("Array compared against 0")
Fixes: c97ee3e0 ("rtw88: add power tracking support")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>