rtw88: Remove unnecessary check code

The rtw_pci_init_rx_ring function is only ever called with a fixed
constant or RTK_MAX_RX_DESC_NUM for the "len" argument. Since this
constant is defined as 512, the "if (len > TRX_BD_IDX_MASK)" check
can never happen (TRX_BD_IDX_MASK is defined as GENMASK(11, 0) or in
other words as 4095).

So, remove this check.

The true motivation for this patch is to silence a false Coverity
warning.

Reviewed-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Len Baker <len.baker@gmx.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20210731163546.10753-1-len.baker@gmx.com