net: tg3: fix redundant check of true expression

Remove the redundant check of (tg3_asic_rev(tp) == ASIC_REV_5705) after
it is checked to be true.

Signed-off-by: Jean Sacren <sakiwit@gmail.com>
Reviewed-by: Michael Chan <michael.chan@broadcom.com>
Link: https://lore.kernel.org/r/20211008063147.1421-1-sakiwit@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>