Remove unnecessary NULL check before freeing using kvfree().
This function will ignore a NULL argument.

Flagged by Coccinelle:

  .../txgbe_hw.c:187:2-8: WARNING: NULL check before some freeing functions is not needed.

No functional change intended.
Compile tested only.
Signed-off-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20240815-txgbe-kvfree-v1-1-5ecf8656f555@kernel.orgSigned-off-by: Jakub Kicinski <kuba@kernel.org>